PSSCMP 2020: Virtual Poster Sessions

Poster Session I (Monday, June 8)

4:15 pm: Anirudha Menon, University of California, Davis. "Role of Disorder in the Physics of Quantum Spin Ice models"

We examine the consequence of disorder on the QSL physics surrounding the pyrochlore-lattice Ising antiferromagnet with random transverse fields. Methods of analysis include Exact Diagonalization, Krylov Space technqiues, and Numerical Linked Cluster (NLC) expansions on finite size clusters (16 and 32 sites). We further restrict to the reduced spin ice manifold in the perturbative regime to incorporate higher system sizes (64 sites), leading to the possibility of a new phase.

1. Tom Pardini, Anirudha Menon, Stefan P. Hau-Riege, and Rajiv R. P. Singh, Phys. Rev. B 100, 144437
2. Anirudha Menon, Tom Pardini, and Rajiv R. P. Singh, Phys. Rev. B 101, 184423


4:20 pm: Benedikt Placke, Max Planck Institute for the Physics of Complex Systems. "Hierarchy of energy scales in field-tunable order by disorder in dipolar-octupolar pyrochlores"
A uniform field on pyrochlore magnets is well-known to act in complex ways on account of the non-collinearity of the easy axes on different sublattice. A magnetic field in the (110) direction thus yields a subextensive classical ground-state degeneracy. We discuss the lifting of this classical degeneracy by quantum fluctuations, mapping out the ground-state phase diagram as a function of the exchange couplings, using linear spin wave theory and real-space perturbation theory techniques.


4:25 pm: Ningxin Jiang, Georgia Institute of Technology. "Synthesis of a d1-titanium fluoride kagome lattice antiferromagnet"
The spin-1/2 kagome lattice antiferromagnet (KLAF) has remained difficult to synthesize. A d1-titanium fluoride KLAF, (MA)2NaTi3F12, with only one crystallographically distinct Ti3+ site has been prepared. No long-range magnetic ordering has been observed down to 0.1 K. Despite the frequency dependence of the a.c. susceptibility, the unusual specific heat behavior at low temperature suggests that this compound could be a potential quantum spin liquid.


4:30 pm: Pavel Volkov, Rutgers University. "Magnon Bose-Einstein Condensation and Superconductivity in a Frustrated Kondo Lattice"
Motivated by the possibility of realizing novel types of magnetic phases and metallic quantum criticality in frustrated Kondo lattice systems, we study a one-dimensional model with a nonmagnetic valence bond solid ground state doped with itinerant fermions. We explore the phase diagram of the model demonstrating the presence of a magnetic-field tuned magnon BEC transition that remains stable in the presence of a Fermi sea and spin-fluctuations driven unconventional superconductivity.


4:35 pm: Chunxiao Liu, University of California, Santa Barbara. "Magnetic structure of a family of frustrated triangular-lattice antiferromagnet with applications to spin liquid candidate NaYbO2"
This poster presents a joint experimental and theoretical work on the spin liquid candidate NaYbO2, which reveals a quantum disordered ground state at zero field and a three sublattice ordered state under field. We find the field induced order can be well described by a 2D XXZ Hamiltonian, obtained the complete phase diagram in field, and confirms the disordered behavior of the zero field state.


4:40 pm: Ana-Marija Nedic, Iowa State University. "Magnetic behavior of multiorbital model of SrCoAs2" 
We studied the magnetic fluctuations in the paramagnetic state of SrCo2As2 from the itinerant approach. We studied a phase diagram depending on the doping, temperature, and internal interaction parameters. The dominant magnetic fluctuations we found are in agreement with inelastic neutron scattering experiments and we can explain the ferromagnetic order in the electron doped, as well as the lack of ordering in the hole doped compound.

4:45 pm: Kisung Kang, University of Illinois at Urbana-Champaign. "Density Functional Theory Study of Magnetocrystalline Anisotropy in Antiferromagnetic Fe2As"
The metallic band structure and easy-plane magnetism of antiferromagnetic Fe2As bring the attention due to electrical switching. The first-principles study of magnetocrystalline anisotropy can provide the contributions of spin-orbit and magnetic dipole-dipole interactions to magnetocrystalline anisotropy. In this study, we calculate the contributions of out-of-plane and in-plane anisotropy and demonstrate their symmetry. The potential switching and thermal stability of Fe2As are addressed.

4:50 pm: Michael Smith, University of Washington. "Giant Magnetoconductivity in Non-Centrosymmetric Superconductors"
We discuss a new contribution to the magnetoconductivity in non-centrosymmetric superconductors that arises via the Debye mechanism. This new contribution is proportional the inelastic quasiparticle relaxation time, and therefore it may significantly exceed the typical contribution to the conductivity as conventionally the inelastic relaxation time is several orders of magnitude larger then the elastic relaxation time.



Poster Session II (Tuesday, June 9)

4:15 pm: Joris Carmiggelt, Delft University of Technology. "High room-temperature valley polarization in chemically-doped monolayer WS2"
Chiral optical selection rules allow for the valley-selective excitation of excitons in TMD monolayers, making these materials a promising opto-valleytronic platform at low temperatures. Unfortunately, high valley polarization at room temperature is rarely reported. We use chemical doping to create trions in monolayer WS2 with a valley polarization of 40% under ambient conditions. After doping also excitons have a high valley polarization, which we attribute to non-radiative decay into trions.

4:20 pm: Chunli Huang, University of Texas at Austin. "Quantum Hall magnets in graphene: Theory of spin-injection"
Nonlocal electrical measurements have revealed intriguing spin transport properties of graphene in the quantum Hall limit. Using spin-polarized chiral edge states and a nonlinear sigma model, we formulate a theory of spin-injection in graphene quantum Hall magnets. We found the ubiquitous saturation of nonlocal signal at large bias voltage observed in experiment is a result of magnon saturation near the injection/detection contacts.

4:25 pm: Nemin Wei, University of Texas at Austin. "Quantum Hall magnets in graphene: theory of magnon-transmission"
Recent nonlocal electrical measurements have revealed remarkable spin transport properties in the monolayer graphene that host various quantum Hall(QH) magnetic states. It was found that magnons generated in the QH ferromagnets at filling factor \nu=1 hardly transmit through the antiferromagnetic state at \nu=0. We use Time Dependent Hartree Fock theory to simulate propagation of magnons through junctions of QH magnets and provide a simple explanation to the lack of magnon transmission at \nu=0.

4:30 pm: Yayun Hu, Pennsylvania State University. "Kohn-Sham Theory of the fractional quantum Hall effect and the abelian anyons"
We formulate the Kohn-Sham (KS) equations for the fractional quantum Hall effect by mapping the original electron problem into an auxiliary problem of composite fermions that experience a density-dependent effective magnetic field. Self-consistent solutions demonstrate that our formulation captures not only configurations with nonuniform densities but also topological properties such as fractional charge and fractional braid statistics. Generalized treatments to the anyons are also discussed.

1. Yayun Hu and J. K. Jain, Phys. Rev. Lett. 123, 176802; Yayun Hu, J. K. Jain, G. Murthy, and S. Rao, unpublished. 

4:35 pm: Md Shafayat Hossain, Princeton University. "Observation of Bloch ferromagnetism of composite fermions"
The ground state of a dilute fermionic system is predicted to be spin polarized. Since this prediction made by Bloch in 1929, this spontaneous ferromagnetism has eluded experimental observations. Here we report such a phase in an interacting composite fermion (CF) Fermi sea at the half-filled Landau level. Our findings highlight the role of CF-CF interaction contrasting the long-believed picture of non-interacting CFs and pave the way for future research on strongly correlated CF phases.

4:40 pm: Denis Candido, University of Iowa. "Predicted strong coupling of solid-state spins via a single magnon mode"
Here we propose a practical setup to create strong coherent coupling between NV centers mediated by a magnon mode of the low loss organic magnetic material V[TCNE]x. We predict that the spin-magnon-mode coupling strength is ∼10 kHz, with corresponding cooperativity C=6 for isotopically pure 12C diamond. Thus our proposal describes a practical pathway for single-spin-state-to-single-magnon-occupancy transduction and for entangling NV centers over micron length scales.


4:45 pm: Martin Lonsky, University of Illinois at Urbana-Champaign. "Skyrmion Breathing Modes in Synthetic Ferri- and Antiferromagnets"
We present micromagnetic simulations of the dynamic GHz-range resonance modes of skyrmions excited by ac magnetic fields in synthetic ferri- and antiferromagnetic trilayer structures. The observed features in the power spectra exhibit a systematic dependence on the interlayer exchange coupling and are related to pure in-phase and anti-phase breathing modes as well as to hybridizations of breathing and spin-wave modes that are characteristic for the considered circular-shaped geometry.

4:50 pm: Nitish Mathur, University of Wisconsin-Madison. "Magnetic skyrmions in nanostructures of non-centrosymmetric materials"
Magnetic skyrmions are a new form of magnetic ordering with whirlpool-like spin arrangements. Confining magnetic skyrmions in nanostructures leads to interesting fundamental insights into skyrmion stability and could provide convenient platforms for potential practical applications of skyrmions in information storage technology. In this poster, I summarize recent studies on electrical detection of magnetic skyrmions in noncentrosymmetric nanostructures made via bottom-up synthesis.

1. N. Mathur, M. J. Stolt, and S. Jin. Magnetic skyrmions in nanostructures of non-centrosymmetric materials. APL Materials, 7(12):120703, 2019

4:55 pm: Tyler Cochran, Princeton University. "Spectroscopic studies of magnetic kagome topological materials"
In magnetic materials, topological properties can be linked to both the magnetic order and the crystal structure. In this short presentation, I contrast recent spectroscopic experiments on two ferromagnetic crystals: isolated kagome crystal structure in TbMn6Sn6 and the 3D kagome structure of Co3Sn2S2. While TbMn6Sn6 manifests a gapped Chern phase, experiments on Co3Sn2S2 are most convincingly described by a gapless Weyl loop phase, much like previously studied Co2MnGa.


Poster Session III (Thursday, June 11)

4:15 pm: Yahui Zhang, Harvard University. "Electrical detection of spin liquids in double moire layer"
Although spin is a fundamental quantum number, measuring spin transport in traditional solid state systems is extremely challenging. This poses a major obstacle to detecting interesting quantum states including certain spin liquids. In this paper we propose a platform that not only allows for the electrical measurement of spin transport, but in which a variety of exotic quantum phases may be stabilized.


4:20 pm: Zhu-Xi Luo, University of California, Santa Barbara. "Moire magnets"
We introduce a general framework to study moiré structures of two-dimensional Van der Waals magnets using continuum field theory. The formalism eliminates quasiperiodicity and allows a full understanding of magnetic structures and their excitations. In particular, we analyze in detail twisted bilayers of Néel antiferromagnets on the honeycomb lattice. A rich phase diagram with noncollinear twisted phases is obtained, and spin waves are further calculated.


4:25 pm: Shaowen Chen, Columbia University. "Electrically tunable correlated and topological states in twisted monolayer-bilayer graphene"
We report the system of twisted monolayer-bilayer graphene (tMBG), where the phase diagram approximates that of twisted bilayer or twisted double bilayer graphene depending on the electric field direction. In the latter case, we observe the emergence of electrically tunable ferromagnetism at one-quarter filling of the conduction band, with a large associated anomalous Hall effect. Uniquely, the magnetization direction can be switched purely with electrostatic doping at zero magnetic field.

1. Chen et al. arxiv 2004.11340 (2020).
2. Yankowitz et al. Science 363, 1059-1064 (2019). DOI: 10.1126/science.aav1910


4:30 pm: Antonio Manesco, University of Sao Paulo. "Magnetic superlattices from elastic Landau levels in graphene/NbSe2 heterostructures"
We show that a hybrid graphene/NbSe2 multilayers yields the formation of a periodically modulated ferrimagnetic groundstate, emerging from an elastic pseudo Landau level, controllable by the application of external electric fields. Our results build on top of recent experimental findings reporting that, when placed on top of a NbSe2 substrate, graphene sheets relax forming a periodic, long-range buckling pattern caused by the lattice mismatch.


4:35 pm: Zeyu Hao, Harvard University. "'Tunable Spin-polarized Correlated States in Twisted Double Bilayer Graphene"
Employing vdW heterostructures of twisted double bilayer graphene (TDBG), we demonstrate a flat electron band that is tunable by perpendicular electric fields in a range of twist angles. Correlated insulating states emerge at quarter- and half-filling and show ferromagnetic order. Upon doping the half-filled insulator, a critical behavior shows in a small area in the density-electric field plane, and is attributed to a phase transition from a normal metal to a spin-polarized correlated state.

4:40 pm: En-Min Shih, Columbia University. "Correlated states in twisted bilayer transition metal dichalcogenides"
We report transport measurements of twisted bilayer tungsten diselenide. We observe low-energy flat bands persisting over twist angles ranging from at least 4 to 5.1 degrees, limited only by contact and dielectric properties. A correlated insulator appears at half band filling that can be sensitively tuned with a combination of twist angle and displacement field.

1. arXiv:1910.12147

4:45 pm: Nicolas Morales-Duran, University of Texas at Austin. "Metal insulator transition in TMD heterobilayers"
A moiré superlattice is formed in twisted transition metal dichalcogenide heterobilayers, giving rise to an isolated flat band for a range of twist angles. This isolated band can be described by a triangular Hubbard model, providing a tunable platform to study the interplay between strong correlations and frustration. In this work, we use exact diagonalization to study the nature of the metal insulator transition that happens in these moiré bands at half-filling.

1. Phys. Rev. Lett. 121, 026402

4:50 pm: Celia González Sánchez, Universidad Autónoma de Madrid. "Development of nano-devices based on few-layer transition metal dichalcogenides (TMDCs)"
Materials with flat energy bands can exhibit xotic quantum phases driven by electronic interactions. These bands have primary been realized in graphene-based heterostructures using the twist angle as tuning parameter. However, TMDCs are also potential candidates for fabricating and exploring the properties of 2D twisted heterostructures. Here, we take the first steps towards the development of devices based on 2D MoS2 and WSe2:thermal annealing, encapsulation with h-BN and graphite contacts.

4:55 pm: Eric Bobrow, Johns Hopkins University. "Exact results on itinerant ferromagnetism and the 15-puzzle problem"
We apply a result from graph theory to prove exact results about itinerant ferromagnetism. Nagaoka's theorem is extended to all nonseparable graphs except single polygons with more than four vertices by mapping to the generalized 15-puzzle problem. This proves that the ground state of a U→∞ Hubbard model with one hole away from half filling on a two-dimensional honeycomb lattice or a three-dimensional diamond lattice is fully spin polarized.


Poster Session IV (Friday, June 12)

2:15 pm: Joshua Heath, Boston College. "Observation of a weakly-correlated Majorana liquid in the silver-lithium iridate Ag3Lilr2O6"
It is well known that the spin liquid phase of Kitaev magnets can be solved analytically by mapping the localized spins into itinerant and localized Majorana excitations. In this work, we describe the Sommerfeld coefficient and quadratic T-dependence in the specific heat of Ag3LiIr2O6 via a Landau-Majorana liquid theory. Agreement with recent experiments suggests that such iridates host an exotic metallic phase. Co-Authors: Faranak Bahrami, Kevin Bedell, Roman Movshovich, & Fazel Tafti

1. "Exotic quantum statistics and thermodynamics from a number-conserving theory of Majorana fermions", by Joshuah T. Heath & Kevin S. Bedell. Journal of Physics A: Mathematical and Theoretical, Volume 52, Number 31:
2. "Thermodynamic Evidence of Proximity to a Kitaev Spin Liquid in Ag3LiIr2O6", by Faranak Bahrami, William Lafargue-Dit-Hauret, Oleg I. Lebedev, Roman Movshovich, Hung-Yu Yang, David Broido, Xavier Rocquefelte, & Fazel Tafti. Phys. Rev. Lett. 123, 237203 (2019):

2:20 pm: Qingdong Jiang, Stockholm University. "From Casimir effect to Quantum Atmosphere"
In 2019, Frank Wilczek and I proposed the new concept "Quantum atmosphere", which opens a new way for probing symmetries and topologies. Here, I will briefly introduce this concept, and how it emerges during our studies on Casimir effects.



2:25 pm: Jiaxin Yin, Princeton University. "Spin-orbit quantum impurity in a topological magnet" 
We use spin-polarized scanning tunneling microscopy/spectroscopy to study the engineered atomic impurity state in a topological magnet. Our work demonstrates the strong spin-orbit effect of the single-atomic impurity at the quantum level, suggesting that a nonmagnetic impurity can introduce spin-orbit coupled magnetic resonance in topological magnets.

2:30 pm: Valentine Volobuev, Polish Academy of Sciences. "Magnetic doping and Rashba effect on surface of topological crystalline insulator Pb1-xSnxSe epilayers"
Band structure at the TI/magnetic material interface is of importance for charge-spin interconversion. The evolution of ARPES spectra of (111) and (001) PbSnSe surfaces after submonolayer thick Fe and Mn deposition is investigated. In addition to TSS, formation of Rashba splitting in conduction band is observed on (111) surface. The resulting Rashba parameter can be tuned over a wide range from 0 to 2 eV·Å by changing of transition metal thickness. No Rashba effect is observed on (001) surface.

1. Volobuev, Valentine V., et al. "Giant Rashba Splitting in Pb1–xSnxTe (111) Topological Crystalline Insulator Films Controlled by Bi Doping in the Bulk." Advanced Materials 29.3 (2017): 1604185.

2:35 pm: Canon Sun, Johns Hopkins University. "Monopole charge denisty wave states in Weyl semimetals"
We study a class of topological charge density wave states exhibiting monopole harmonic symmetries. When electron and hole Fermi surfaces carry different Chern numbers, the particle-hole pairing exhibits a nontrivial Berry phase inherited from band-structure topology independent of the concrete density wave ordering mechanism. The associated density wave gap functions become nodal, and the net nodal vorticity is determined by the monopole charge of the pairing Berry phase.


2:40 pm: Arun Ramanathan, Georgia Institute of Technology. "Kitaev material candidates beyond the Iridates" 
Na2MO3 based Mott insulators have been studied recently as potential candidates to realize Kitaev spin model. However, candidates to realize the Kitaev spin model are limited to 4d/5d systems. Lanthanide (Ln) elements with significant SOC can also be considered in this context. In this talk, I will present our work on a new lanthanide-based, Kitaev material candidate with a potential Jeff=1/2 ground state.

2:45 pm: Pontus Laurell, Oak Ridge National Laboratory. "Applying entanglement witness to neutron scattering data on a quantum magnet"
Many quantum states of matter have interesting entanglement properties. However, the study of entanglement in condensed matter has largely remained a theoretical endeavor, due to the difficulty of directly measuring it. Here, in a combined density-matrix renormalization group and neutron scattering study, we demonstrate that entanglement witnesses can be extracted from inelastic neutron scattering data and used to detect and quantify entanglement in an S=1/2 Heisenberg antiferromagnetic chain.

2:50 pm: Jonathan Gibbons, University of Illinois at Urbana-Champaign. "Large Temperature-Dependent Spin Torque Efficiency in FeRh" 
FeRh has complex anti-ferromagnetic ordering, which can break symmetries that ordinarily forbid exotic spin torques. We have characterized the damping-like torque generated in FeRh via DC-biased spin torque ferromagnetic resonance on FeRh/Cu/Permalloy multilayers. We report a large exotic spin torque efficiency at room temperature in the anti-ferromagnetic state that grows by a factor of several at lower temperatures. Supported by the Q-MEEN-C, an EFRC funded by the U.S. DOE, Office of Science.