Theoretical Quantum Matter

Seminar - Markus Müller (PSI)
2019-08-30 08:00 - 17:00 (Europe/Stockholm)
Speaker: Markus Müller
Affiliation: Paul Scherrer Institut (PSI) in Switzerland

Title: Coherent oscillators, spectral hole-burning and emerging q-bits in rare earth magnets

Abstract: Experiments in rare earth compounds, such as LiHoYF4 and GGG (Gd-Ga-garnet), have demonstrated very long lived, coherent quantum degrees of freedom with sharply defined excitation energies, many orders of magnitude below the scale of typical magnetic interactions (exchange, dipolar or hyperfine interactions), and with life times on the order of seconds.
The nature of these coherent entities in the midst of a solid state environment has remained a mystery for a long time. I will discuss their likely origin and argue that they arise from an intricate interplay between several nuclear and electronic spins, and exist only in long lived states out of equilibrium. The sharpness of the excitations is protected by Anderson localization of composite objects, with an unusual type of power law hopping. The emerging, well isolated degrees of freedom may be promising candidates for magnetic qubits.
Time permitting I will discuss ideas of how to realise quantum memories and gates based on electro-nuclear qubits in rare earth systems.

Odd-Frequency Meeting in Uppsala
2019-09-02 | Uppsala University, Uppsala, Sweden

[Talk] Shota Kanasugi - Spin-orbit-coupled ferroelectric superconductivityand multiorbital effects in SrTiO3
2019-09-03 10:00 - 11:00 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden
Speaker: Shota Kanasugi
Affiliation: Kyoto University
Title: Spin-orbit-coupled ferroelectric superconductivityand multiorbital effects in SrTiO3
Abstract: A lot of exotic superconducting statesemerge close to other ordered phases, such as anisotropic superconductivity in cuprates. Although previous studies have mainly focused on the superconductivityclose to magnetic instability, the ferroelectric (FE) counterpart is recently receiving increased attention since such superconductivity was reported in doped SrTiO3(STO). STO is a unique compound which exhibits both quantum paraelectricity and superconductivity. The superconducting transition temperature is enhanced in the vicinity of the FE quantum critical point [1-4]. Moreover, recent experiments suggest the coexistence ofsuperconductivity and ferroelectricity in doped STO [2]. These results imply a cooperative correlation between superconductivity and ferroelectricity against a long-held belief that they should be incompatible.In this talk, we present that aFE-like polar inversion symmetry breaking order can be controlled by the superconductivityin spin-orbit coupled systems. We introduce a model of electron-lattice coupled two-dimensional superconductor,in which the ferroelectricity-induced Rashba spin-orbit coupling [5]is included. It is shown that the FE superconductivity,which is characterized by a FE structural transition in the superconducting state,is realized through two different mechanisms [6]. First, the FE superconducting state is stabilized by the Lifshitz transition of the Rashba split bandsin lowcarrier density regimes.Second, the FE superconductingstate is stabilized under a Zeeman magnetic field, thanksto the suppressionof the Pauli depairingeffect in the FE phase. Furthermore, we show that the FE superconductivity in bulk STO is strongly affected by the multiorbital effectoft2gelectrons[7]. Then, we predict a topologicalWeyl superconducting state in the FE superconducting phase of bulk STO.
References
[1] A. Stucky et al., Sci. Rep. 6,37582 (2016).
[2] C. W. Rischau et al., Nat. Phys. 13, 643 (2017).
[3] Y. Tomioka et al., Nat. Commun. 10, 738 (2019).
[4] K. Ahadi et al., Sci. Adv. 5, eaaw0120 (2019).
[5] G. Khalsa, B. Lee, and A. H. MacDonald, Phys. Rev. B 88, 041302 (2013).
[6] S. Kanasugi and Y. Yanase, Phys. Rev. B 98, 024521 (2018).
[7] S. Kanasugi and Y. Yanase, arXiv: 1904.11113 (2019)

[CMT SEMINAR] Ipsita Mandal - Some aspects of correlated electrons
2019-09-03 11:00 - 12:00
Speaker: Ipsita Mandal

Affiliation: University of Stavanger,

Title: Some aspects of correlated electrons,

Time: Fika 10:30-11:00 , Seminar 11:00-12:00,
Place: Nordita South, room 112:028 .

Abstract:
In this talk, I am going to present exciting results from two of my ongoing/recent projects.
First part:
Spin-orbit coupling (SOC) assisted (spin j = 1/2) Mott insulators exhibiting bond-directional exchange interactions are expected to exhibit unconventional quantum magnetic phases like spin liquids [1, 2] predicted by the Kitaev model, dubbed as Kitaev spin liquid (KSL). The feature of a Kitaev material is that the Kitaev coupling is the dominant exchange coupling. Compounds like honeycomb iridates and α-RuCl_3 have been identified as candidate Kitaev materials. In the first part of my talk, I will address the unresolved question whether α-RuCl_3 is actually a Kitaev material. If yes, what is the value of the Kitaev coupling strength? If not, what are the dominant terms in the effective spin Hamiltonian that can describe the system? We focus on the results from resonant torsion magnetometry experiments by Modic et al, which they can measured the magnetotropic coefficient k, when a magnetic field B is applied making angle θ with the c-axis of the crystal. Using a simple Hamiltonian with a dominant paramagnetic term, we will show that we can fit the data obtained in the experiments.

Second part:
In sufficiently clean metals, it is possible for electrons to collectively flow as a viscous fluid at finite temperature. These viscous effects have been predicted to give a notable magneto resistance, but whether the magnetoresistance is positive or negative has been debated. We argue that regardless of the strength of inhomogeneity, bulk magnetoresistance is always positive in the hydrodynamic regime.

[Talk] Manuel Simonato - On the Spectral Properties of Inhomogeneous Luttinger Liquids
2019-09-03 12:00 - 13:00 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden
Speaker: Manuel Simonato
Title: On the spectral properties of inhomogeneous Luttinger liquids
Abstract: The physics of one-dimensional systems of interacting fermions strongly differs from the picture offeredby Fermi liquid theory. The low-energy properties of metallic, paramagnetic 1D Fermi systems arewell described by the Luttinger liquid (LL) theory. Among other properties, the homogeneous LL isknown to exhibit power-law behaviour for various correlation functions. For spin rotational invariantmodels, the exponents can be expressed in terms of a single parameterKρ, which is known to benon-universal.The LL concept emerged in the study of homogeneous systems with periodic boundary condition(PBC). In these models thelocal spectral functionshows a power-law suppression at energies asymp-totically close to the chemical potentialμ. Theoretically, this is very well understood and the exactLL parameterKρis known for a set of integrable models. In the last decades however, the interestshifted towards the investigation of LLs with PBC including impurities. The fact that these systemshave been shown to scale to chains with open ends led to the study of several models where openboundary condition (OBC) are introduced. As the translational invariance is broken, the exponent ofthe power-law suppression close to the boundary differs from the one in the bulk.The present work is devoted to the study of the local spectral function of two lattice models of LLswith open boundaries, namely the spinless fermions model with nearest neighbour interaction and the1D Hubbard model, with the methods of perturbation theory. It is demonstrated that many aspectsof the spectral properties can be understood within the HF theory. Despite what one usually readsabout one-dimensional interacting Fermi systems,in the presence of the boundaryperturbation theoryis already capable of providing meaningful results. Concurrently, this method also allows us to developan understanding of the dip appearing in the local spectral function at an energy different from thechemical potential.

[Group Meeting] Presentation by Roberto Díaz Pérez
2019-09-10 15:00 - 16:00 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden
Title: Machine Learning in Matter at Different Scales

[Group Meeting]
2019-09-17 08:00 - 17:00

[CMT Seminar] Adrien Bouhon - Weyl nodes with non-Abelian charges
2019-09-17 10:30 - 12:00
Speaker: Adrien Bouhon from Nordita

Title: Weyl nodes with non-Abelian charges

Time: Tuesday
17th of September, Fika 10:30-11:00, Seminar 11:00-12:00,

Place: Nordita South, room 112:028 .

Abstract:
Weyl points trapped within a C_2T-symmetric plane (C2 = 180 degrees rotation, and T = time reversal) possess non-Abelian topological charges on top of their chirality. E.g. three-level systems realize the quaternion group. This picture requires to go beyond the modeling of a band structure as a Grassmannian (where a single spectral gap is specified). The non-Abelian nature of Weyl points implies new types of obstruction, where, for instance, two Weyl points with opposite chiralities may not annihilate. Also, the non-Abelian charges can be converted through the braiding of Weyl points in momentum space.

I will review three different yet equivalent ways of computing the non-Abelian charges: (i) as a non-cyclic phase defined from the parallel transport of the Hamiltonian along a base loop, (ii) as the Euler class of a two-band subspace over a patch bounded by the base loop, and (iii) as the winding number of the Pfaffian of the Wilsonnian Hamiltonian – of the two-band subspace – as the base loop flows over the patch.

[Remark: 50% of the material I will present is new as compared to the talk I gave at the Nordita workshop in beginning of August.]

Masters Thesis Defence - Roberto Díaz Pérez
2019-09-19 10:00 - 12:00

[Group Meeting] Johan Hellsvik - Impressions from the NNSP-SwedNess Neutron School 2019, Tartu
2019-09-24 15:00 - 16:00 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden
Talk by Johan Hellsvik.
Title: Impressions from the NNSP-SwedNess Neutron School 2019, Tartu
Abstract: The European Spallation Source (ESS) is under development and construction in Lund. The Swedish and international neutron community are running a number of activities and projects in connection to ESS. One such activity is the SwedNess graduate school in neutron scattering. I will give impressions from the NNSP-SwedNess Neutron Summer School 2019, Tartu, and highlight some of the ESS neutron instruments that will be used for condensed matter physics.

[Group Meeting] Sahar Pakdel
2019-10-01 15:00 - 17:00
Sahar Pakdel, Aarhus University (Denmark)
Title: Exploring 2D-materials in synergy with experimentalists!”.

Abstract: I will be talking about my experience studying some 2D systems with experimentalists. Specifically I will stress what I consider as the need for flexibility in the theory side while working on systems that are measured at the same time, in comparison with exploring well-presented data.

[CMT Seminar] Adrian Kantian/ Gunnar Bollmark - 1D electrons coupled to reservoirs: towards new systems of correlated quantum matter and novel devices
2019-10-02 10:30 - 12:00 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden
Speaker: Adrian Kantian and Gunnar Bollmark (Uppsala University)

Title: 1-D electrons coupled to reservoirs: towards new systems of correlated quantum matter and novel devices.

Time: Wednesday, 2nd of October, Fika 10:30-11:00 , Seminar 11:00-12:00,

Place: Nordita South, room 112:028 .

Abstract:
Correlated electrons are at the forefront of condensed matter theory. Interacting quasi-1D electrons have seen vast progress in analytical and numerical theory, and thus in fundamental understanding and quantitative prediction. Yet, in the 1D limit fluctuations preclude important technological use, particularly of superconductors. In contrast, high-Tc superconductors in 2D/3D are not precluded by fluctuations, but lack a fundamental theory, making prediction and engineering of their properties very difficult. In this talk we will present work in progress on combining the advantages of 1D systems with those of higher-dimensional ones, by advancing the theory of quasi-1D electrons coupled to an electron bath. We will focus on two aspects in particular: (1) How to enable a new state of matter, 1D electrons with true superconducting order, by using fluctuations from a coherent electronic reservoir. (2) A new approach for the deliberate engineering of superconducting systems with properties computable, and thus optimisable, ab-initio, i.e. from their microscopic properties. The use of hard-core bosons at this first stage allows us to rigorously validate our approach, which yields insight into the physics of dimensional crossover in strongly correlated many-body systems.

[Seminar] Vladimir Pudalov
2019-10-07 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden
Condensed Matter Seminar Series
Speaker: Vladimir Pudalov, Lebedev Physical Institute
Title:“Thermodynamics of the correlated 2D electron system: Entropy per electron and spin magnetization per electron”

Abstract: In contrast to ubiquitous transport and optical measurements, interpretation of thermodynamic data is straightforward and is often model independent. However, due to the additive character of thermodynamic properties, their measurements for 2D electron systems is rather challenging. I shall report recent advancement in thermodynamic measurements of the correlated 2D electron system. Particularly, I focus on the derivatives of the chemical potential with respect to magnetic field and temperature. The former enables to determine spin magnetization per electron and the latter – entropy per electron.
I shall briefly describe recent results obtained with these technique and their impact on the current understanding of the still debatable problem of the ground state(s) of strongly correlated two-dimensional electron systems.

[CMT Seminar] Joe Bailey - Spin wave dynamics in ultrathin yttriumiron garnet measured with x-ray microscopy
2019-10-08 10:30 - 12:00 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden
Title: Spin wave dynamics in ultrathin yttriumiron garnet measured with x-ray microscopy
Speaker: Joe Bailey, from the PSI (Switzerland)
Time: 10:30-11am Fika / 11-12am Talk
Abstract: Magnonics, the study and development of devices utilising collective spin excitations, is a rapidly growing field, covering both fundamental topics (antiferromagnetism[1], quasiparticle condensates[2]) and technological applications (MRAM[3], spintronics[4]). Yttrium iron garnet (YIG) is a ferrimagnetic insulator with the lowest known magnon damping factor of any material [5]. This low damping leads to a prevalence of nonlinear effects and notably the room temperature Bose-Einstein condensation (BEC) of magnons first reported by Demokritov et al in 2006[6], and subject of a number of investigations since[7]-[10]. Ultrathin structures will be required for applications butremainlargelyunexplored. Here I report on the design, fabrication and characterization of microwave devicesbased on such ultrathin structures(YIG thickness~100nm).The spin wavedynamics weremeasured using both Brillouin Light Scattering (BLS) and time resolved scanning transmission x-ray microscopy(TR-STXM), locked in phase with microwave stimulation of the devices.Anumber of milestonesare reached for our novel devices.First, we have explicitly measuredthe spin wave dispersion in YIG[11], and demonstratedthe existence of the finite momentum minimum required for magnon BEC. Second, the BLSdata demonstratethat the condensate exists in our samples. These results are a key development towards addingcondensate phenomena to the thin film magnonics toolbox.

Nobel Prize Announcement - Colloquium
2019-10-08 15:00 - 16:00 | Oskar Klein Auditorium, Albanova Campus
Details: TBA
https://www.kva.se/en/pressrum

[Group Meeting] Adrien Bouhon - Weyl Nodes with Non-Abelian Charges
2019-10-08 16:15 - 17:00
Abstract:
Weyl points trapped within a C_2T-symmetric plane (C2 = 180 degrees rotation, and T = time reversal) possess non-Abelian topological charges on top of their chirality. E.g. three-level systems realize the quaternion group. This picture requires to go beyond the modeling of a band structure as a Grassmannian (where a single spectral gap is specified). The non-Abelian nature of Weyl points implies new types of obstruction, where, for instance, two Weyl points with opposite chiralities may not annihilate. Also, the non-Abelian charges can be converted through the braiding of Weyl points in momentum space.

I will review three different yet equivalent ways of computing the non-Abelian charges: (i) as a non-cyclic phase defined from the parallel transport of the Hamiltonian along a base loop, (ii) as the Euler class of a two-band subspace over a patch bounded by the base loop, and (iii) as the winding number of the Pfaffian of the Wilsonnian Hamiltonian – of the two-band subspace – as the base loop flows over the patch.

[Group Meeting]
2019-10-15 15:00 - 16:00 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden

Nordita-KTH Applied Physics Annual Meeting 2019
2019-10-25 10:00 - 17:00 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden
Webpage of event can be found here
This meeting is intended as a platform of discussion to set up collaborations on KAW (The Knut and Alice Wallenberg Foundation) and future projects.
Schedule
The event will comprise of introductory talks on the theory and experimental side, intended to last fifteen minutes and open to the floor for discussion for another fifteen minutes, followed by lunch and discussion about overlap and potential collaborations.
On the theory side
The Dirac Materials group will ensure the main core skills of our expertise are showcased to the experimental participants or other theoretically-minded participants.

Habib Rostami / Pavlo Sukhachov – Optics and strain effects in TMDs.
David Carvalho – Light-Matter Interactions in Dirac Materials
Bart Olsthoorn – Machine Learning in Material Informatics and Spectroscopy

12.30 – Lunch

On the experimental side
TBC

Collaboration and overlap discussions. (flexible timing)

Group Meeting
2019-10-29 10:00 - 11:00 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden

[CMT] Ilaria Maccari - Vortex physics in 2D disordered superconductors
2019-10-29 10:30 - 12:00
Speaker: Ilaria Maccari (KTH)

Title: Vortex physics in 2D disordered superconductors

Time: Tuesday 29th of October, Fika 10:30-11:00 , Seminar 11:00-12:00,

Place: Nordita South, room 112:028 .

Abstract:
The study of quasi-two-dimensional (2D) superconductors can hardly avoid to take into account the presence of vortices. Many real systems, of both conventional and unconventional superconductors, undergoes the superconductor-insulator transition via the Brezinskii-Kosterlitz-Thouless (BKT) transition, at which the phase coherence of the condensate is destroyed by means of free-vortices proliferation.
When a finite flux of the magnetic field is applied to the films, the role of vortices becomes even more crucial for the understanding of the superconducting (SC) transition. Indeed, in this case, the transition is no longer driven by the vortex-antivortex unbinding, but rather by the melting of the 2D Abrikosov lattice of vortices. Such melting, as predicted by the BKT theory, afterward refined by Halperin, Nelson and Young (BKTHNY), can occur in two steps via an intermediate state called hexatic phase. In real systems, the observation of the two-step BKTHNY melting could be hindered by the presence of additional ingredients, such as random pinning, and also competing phases. In [1], we have shown that the 2-dimensional vortex lattice in the a-MoGe thin films follows the BKTHNY sequence of melting as the magnetic field is increased. Identifying the signatures of various transitions on the bulk transport properties of the superconductor, we construct a vortex phase diagram for a 2D superconductor. From a theoretical standpoint, the classical XY model with a transverse magnetic field is a very promising candidate to capture the physics experimentally observed and to explore stronger disorder regimes. It constitutes hence a perfect playground for the investigation of the long-standing issue of the emergent glassy-state of the vortex lattice in the presence of disorder.

[1] I. Roy, S. Dutta, A. N. Roy Choudhury, S. Basistha, I. Maccari, S. Mandal, J. Jesudasan, V.Bagwe, C. Castellani, L. Benfatto, P. Raychaudhuri, Phys. Rev. Lett. 122 (4), 047001 (2019)

[CMT] Sumanta Bandyopadhyay - Entangled Pauli Principles: the DNA of Quantum Hall Fluids
2019-11-05 10:30 - 12:00 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden
Speaker: Sumanta Bandyopadhyay (NORDITA)

Title: Entangled Pauli Principles: the DNA of Quantum Hall Fluids

Time: Tuesday 5th of November, Fika 10:30-11:00 , Seminar 11:00-12:00,

Place: Nordita South, room 112:028 .

Abstract:
A formalism is developed for the rigorous study of solvable fractional quantum Hall parent Hamiltonians with Landau level mixing. The idea of organization through “generalized Pauli principles” is expanded to allow for root level entanglement, giving rise to “entangled Pauli principles”. Through the latter, aspects of the effective field theory description become ingrained in exact microscopic solutions for a great wealth of phases for which no similar single Landau level description is known. We discuss in detail braiding statistic, edge theory, emergent ground state symmetry and rigorous zero mode counting from a microscopic Hamiltonian in a strongly correlated system. We will further discuss the several other application of this methodology in finding parent Hamiltonian for composite fermion.

Group Meeting
2019-11-05 15:00 - 16:00

[CMT] Xiao-Jia Chen - Discovery of Superconductivity in Phenyl Molecules
2019-11-06 10:30 - 12:00 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden
Speaker: Xiao-Jia Chen (Center for High-Pressure Science & Technology Advanced Research)

Title: Discovery of superconductivity in phenyl molecules

Time: Wednesday 6th of November, Fika 10:30-11:00 , Seminar 11:00-12:00,

Place: Nordita South, room 112:028 .

Abstract:
Organic compounds are always promising candidates of superconductors with high transition temperatures Tc’s. In this talk, we will first talk about our recent discovery of superconductivity with Tc’s as high as 123 K in polyparaphenylene oligomers. Then we will show the experimental realization of superconductivity in other phenyl molecules such as organometallic compounds or compounds only containing C, H, and N. The evidence of the appearance of superconductivity is provided by the observations of the measurements of the dc and ac magnetic susceptibility and resistivity measurements together with the opening of superconducting gap detected from Raman spectroscopy. The obtained superconducting parameters classify these phenyl molecules as type-II superconductors. The benzene ring is identified to be the essential superconducting unit in such phenyl compounds. The superconducting phases and their composition are determined by the combined studies of the X-ray diffraction and theoretical calculations as well as the Raman spectroscopy measurements. The easy processability, light weight, durability of plastics, and environmental friendliness of these new phenyl superconductors have great potential for the fine-tuning of electrical properties. This discovery opens a window for exploring superconductivity in phenyl molecules.

Whiteboard discussion - Dirac Materials group & Xiao-Jia
2019-11-07 14:00 - 15:00

[Colloqium] David Cassidy - Recent experimental progress in positronium-laser physics
2019-11-07 15:00 - 16:00
Speaker: David Cassidy from the University College London.
Title: Recent experimental progress in positronium-laser physics
Time and place: Thursday November 7 at 15.15 (coffee and tea from 15.00) in the Oskar Klein auditorium FR4.
Abstract:
The field of experimental positronium physics has advanced significantly in recent years, in many cases by employing new techniques for trapping and manipulating positrons using Surko-type buffer gas traps [1]. These devices capture and store positrons, allowing for the production of high quality DC beams, or high intensity pulsed beams. The latter approach can be used to create an instantaneous cloud of Ps atoms that can be probed with standard ns pulsed lasers. This allows for the optical production of excited Ps states, ranging from 2P levels, which decay back to the ground state in 3.2 ns, to metastable 2S states, that cannot decay radiatively, but will self-annihilate (in 1.1 microseconds), to long-lived Rydberg states, that do not annihilate at all and, for easily produced states, may have radiative lifetimes of hundreds of microseconds [2]. The ability to generate Ps atoms in excited states facilitates numerous experimental programs [3], including precision optical and microwave spectroscopy and the application of Stark deceleration methods to guide, decelerate and focus Rydberg Ps beams. In this talk I will discuss recent examples of such experiments and what may be possible in the near future.
References
[1] Plasma and trap-based techniques for science with positrons, J. R. Danielson, D. H. E. Dubin, R. G. Greaves, and C. M. Surko, Rev. Mod. Phys. 87, 247 (2015).
[2] Measurement of Rydberg positronium fluorescence lifetimes, A. Deller, A. M. Alonso, B. S. Cooper, S. D. Hogan, and D. B. Cassidy, Phys. Rev. A 93, 062513 (2016).
[3] Experimental progress in positronium laser physics, D. B. Cassidy, Eur. Phys. J. D 72, 53 (2018).

Ren-Shu Wang - Exploring superconductivity in organobismuth molecules
2019-11-07 16:15 - 16:45 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden
Exploring superconductivity in organobismuth molecules

Ren-Shu Wang
Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China

Recently, novel quantum phenomena such as topological insulators and superconductors were suggested in organometallic materials. Three different types of organobismuth molecules, including triphenylbismuth (TPB), tri-p-tolylbismthine (p-TTB), and tri-o-tolylbismthine (o-TTB), were investigated to explore organic superconductivity by alkali metal doping. The target organic molecules have similar structures, expect for the type and the position of the functional group. The dc and ac magnetic susceptibility, and electrical resistivity measurements reveal that all these doped molecules exhibit superconductivity, and their Tc’s vary from 3.5 (and/or 7.2) to 3.6 (and/or 5.3) and 3.6 K for K-doped TPB, p-TTB, and o-TTB, respectively. The shield fractions (SFs) of the main superconducting phases at 1.8 K are 3.74%, 18%, and 17% for K-doped TPB, p-TTB, and o-TTB, respectively. In comparison with TPB, adding the -CH3 groups in p-TTB and o-TTB do not make much difference for Tc of main phase rather than bringing about the increase of the SF, indicating that the simple addition of functional groups is an effective way to tune (super)conductivity in such materials. The main superconducting phases and their composition in these molecules are determined by combined studies of X-ray diffraction and theoretical calculations as well as Raman spectroscopy measurements. These findings enrich the applications of organometallic compounds in superconductivity and add a new electron-acceptor family of organic superconductors.

Di Peng - Antiferromagnetic order and possible quantum spin liquid in sodium doped 2,2′-bipyridine
2019-11-07 16:45 - 17:15
Antiferromagnetic order and possible quantum spin liquid in sodium doped 2,2′-bipyridine

Di Peng
Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China

Organic molecular solids with correlated electronics based on π-electron networks provide fertile ground for the search for peculiar materials, including antiferromagnetic and quantum magnetism. We report a development method for doping alkali metals into organic materials and forming a homogeneous phase together with the experimental discoveries of two antiferromagnetic phase in sodium doped 2,2′-bipyridine at different molar ratios. An antiferromagnetic phase of 160 K is found in sodium-doped 2,2′-bipyridine with a molar ratio of less than 1:1. Another antiferromagnetic phase with Neel temperature of 25 K is observed in samples with molar ratios of 1:1 and 1:2. Applying magnetic field can slowly suppress the 160 K antiferromagnetic phase, while the 25 K antiferromagnetic phase is insensitive to the applied field rather than showing an increase of magnetization below 6 K. This behavior is consistent with the characteristics of quantum spin liquid, in which strong quantum fluctuations lead to the disorder at low temperatures. We will discuss more about the experimental details about whether a strong spin frustrated antiferromagnetic phase is formed in sodium-doped 2,2′-bipyridine and whether it enters a quantum spin liquid state at low temperatures.

Group Meeting
2019-11-12 15:00 - 16:00 | NORDITA // South (Meeting Room 112.006B), Roslagstullsbacken 23, Stockholm, 106 91, Sweden
Schedule:
Presentation by Razmik.

[Colloquium] A. Balatsky - Dynamic Quantum Matter
2019-11-14 15:00 - 16:00
Speaker: Alexander Balatsky from NORDITA.

Title: Dynamic Quantum Matter
Time and place: Thursday November 14 at 15.15 (coffee and tea from 15.00) in the Oskar Klein auditorium FR4.

Open Acess Publishing - Peter Mitchell (IntechOpen)
2019-11-20 11:00 - 12:00
Open Access books presentation / Q&A Session

Peter Mitchell (IntechOpen, London)
20 November

You are invited to join a short session with Peter Mitchell from IntechOpen, a start-up publisher specialising in Open Access books and progressive funding models.
The session will cover:

Disseminating your work with impact: the benefits of non-journal Open Access publishing
Funding Open Access, including a new “no-author-fee fund” for physicists, engineers, and computer scientists
Q&A: ask anything about Open Access text and reference, ideas for new works, how to submit a proposal, etc.
