Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session T56: Cooperative Phenomena (Spin Structures, Spin Waves, Phase Transitions) II |
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Sponsoring Units: GMAG Chair: Travis Williams, Oak Ridge National Laboratory Room: Room 304 |
Thursday, March 9, 2023 11:30AM - 11:42AM |
T56.00001: Atomic-Scale Visualization of Magnetic Phase Evolution in GdTe3 Marisa L Romanelli, Arjun Raghavan, Anuva Aishwarya, Julian May-Mann, Anisha G Singh, Maja D Bachmann, Ian R Fisher, Eduardo H Fradkin, Vidya Madhavan Gadolinium tritelluride (GdTe3) is a van der Waals antiferromagnet that has been extensively studied due to its high mobility, incommensurate charge density wave, and pressure-induced superconductivity. However, some aspects of this material’s properties are still not well understood. For example, although it is known that the spins in GdTe3 are oriented in plane at low temperature, the precise nature of the AFM ordering is not known. We use spin-polarized STM to visualize the AFM ordering in GdTe3 at the atomic scale. We also study the evolution of the AFM and CDW orders with temperature to probe the low-temperature phase transitions. Our findings support the picture presented in a recent magnetic susceptibility and specific heat study of this material, which suggested that a canted AFM order with a small ferromagnetic component emerges between 7 and 10 K. |
Thursday, March 9, 2023 11:42AM - 11:54AM |
T56.00002: Temperature- and magnetic field-dependent Raman spectroscopy of ErFeO3 Jeffrey R Simpson, Thuc T Mai, Angela R Hight Walker, Dasom Kim, Junichiro Kono, Wanting Yang, Xiaoxuan Ma, Shixun Cao The recent report[1] of Dicke cooperativity in the magnetic interactions of erbium orthoferrite ErFeO3 as observed in terahertz (THz) spectra stimulates a complementary Raman spectroscopic study. Bulk ErFeO3 forms an orthorhombic perovskite crystal structure, space group Pbnm, and demonstrates antiferromagnet ordering of the Fe3+ spins below the Néel temperature TN~650K, with additional magnetic phases occurring below 85K. A novel, magneto-Raman microscope system affords measurement of low-frequency (down to ~10 cm-1) Raman-active lattice (phonons) and magnetic (magnons) excitations as a function of polarization orientation, temperature (2 to 300)K, and magnetic field (0 to 9)T in either Faraday or Voigt geometry. We discuss the dependence of the observed Raman-active phonons and magnons in b-cut ErFeO3 on polarization, temperature, and magnetic field, specifically, low-temperature and H-field || a. Furthermore, we compare our Raman spectra with THz measurements and predictions from mean-field theory to further elucidate the nature of magnetic interactions in this system. |
Thursday, March 9, 2023 11:54AM - 12:06PM |
T56.00003: Simplifying higher order perturbation theory for effective spin-1/2 models Frank D Wandler, Sreekar Voleti, Arun Paramekanti Magnetic phenomena in Mott insulators are often understood by constructing effective spin-1/2 models. The standard way of determining these spin models is through second order perturbation theory in electron hoppings on a lattice. However, recent work on various d-orbital systems have shown that this approach is insufficient to capture the physics, when the effective spin-1/2 manifold is not well separated from higher energy levels. A recent example is provided by certain double perovskite magnets which feature competing multipolar orders. To overcome these issues there are two main options: to make long, demanding calculations to go to higher orders of perturbation theory or to resort to numerical non-perturbative methods. We propose a novel third option that allows for analytical calculations to be performed more simply. This new approach is a two-step process, where one uses usual second order perturbation theory in the hoppings to find the Hamiltonian for a higher-spin problem, then using perturbation theory to integrate out higher energy/higher spin modes to get an improved spin-1/2 model. Such an improved perturbation theory can totally reorganize which exchange couplings dominate, or can even generate entirely new types of magnetic Hamiltonians. |
Thursday, March 9, 2023 12:06PM - 12:18PM |
T56.00004: Antiferromagnets with non-interconvertible spin motif pair Linding Yuan, Xiuwen Zhang, Alex Zunger Recent findings of the emergent splitting of spin polarized energy bands in antiferromagnets that does not rely on spin-orbit coupling has drawn great attention due to its profound physics and potential applications. Formal symmetry conditions, including both spin symmetry and magnetic symmetry, telling which antiferromagnets would deliver such exotic spin splitting has been worked out by us previously (Phys. Rev. B 102, 014422 (2020); Phys. Rev. Materials 5, 014409? (2021)). However, the symmetry conditions did not amount to a transparent structural chemistry intuition for the enabling principles. Here, by introduce the concept of spin motif pair -- simple pairs of real space structural motifs carrying opposite magnetic moments in the unit cell -- we show the effect enabling antiferromagnets are those with spin motif pair that cannot be interconverted by translation nor spatial inversion. This real space motif approach provides an intuitive way to understand the abstract symmetry rules needed for the antiferromagnetic-induced spin splitting effect. Insights beyond the symmetry offered by the motif on symmetry breaking and momentum dependent spin splitting has been discussed. We envision the motif approach would accelerate intuitive identifications and design of materials having this effect with sizable magnitude. |
Thursday, March 9, 2023 12:18PM - 12:30PM |
T56.00005: Pressure dependence of the helical spin structure in MnP Masaaki Matsuda, Sachith E Dissanayake, Kazuyoshi Yoshimi, Shusuke Kasamatsu, Feng Ye, Songxue Chi, Jinguang Cheng, Jiaqiang Yan, Jun Gouchi, Yoshiya Uwatoko MnP is a metal that shows successive magnetic transitions from paramagnetic to ferromagnetic and helical magnetic phases with decreasing temperature at ambient pressure. With applied pressure, the magnetic transition temperatures decrease and superconductivity appears around 8 GPa where the magnetic order is fully suppressed and the quantum critical behavior is observed [1]. These results suggest that the superconducting pairing mechanism is unconventional and may be relevant to magnetic fluctuations. In order to elucidate the magnetic ground state adjacent to the superconducting phase, high-pressure neutron diffraction measurements have been performed. The helical magnetic structure with the propagation vector along the b axis, reported previously at 3.8 GPa [2], was found to be robust up to 7.6 GPa. Pressure dependences of the magnetic propagation vector, the magnetic transition temperature, and the magnetic moment in the helical phase were elucidated. Furthermore, we performed theoretical calculations to evaluate the frustrated magnetic interactions as a function of pressure and understand how the helical structure is stabilized with applied pressure. |
Thursday, March 9, 2023 12:30PM - 12:42PM |
T56.00006: Multiple Solutions in Crystal Electric Field Simulation via gPy Qianli Ma, Erxi Feng, Xiaojian Bai, Guannan Zhang, Huibo Cao Frustrated magnets with Rare-Earth (RE) elements have attracted intense interest in the condensed matter community due to exhibiting diverse magnetic and quantum behaviors. One of the mechanisms that causes magnetic diversity and complexity is the interaction between the 4f electron shell and the crystal electric field (CEF) generated by surrounding oxygen anions. Although the interactions on magnetic dipole moments can be complicated, there have been considerable success by treating the magnetic dipole moment as an effective spin - 1/2 system in the low energy limit. CEF analysis naturally lies at the center of determining the single ion anisotropy and evaluating the effectiveness of spin-1/2 approximation. It can tell g-tensor that represents the local magnetic anisotropy of a single spin. From here, one can define a Hamiltonian to describe the magnetic system and find the magnetic ground state. Currently, CEF Hamiltonian can be solved based on an effective point charge model, which replies on the good experience in properly assigning point charges around the RE to reach a reliable solution. Direct fitting of the CEF Hamiltonian at a low point-group symmetry position can be challenge due to more refinable parameters than that can be obtained from resolution limited experimental data. We have developed a Python3 based method, named as gPy, to efficiently survey large CEF parameter phase space and find the CEF parameter sets and corresponding g-tensor that best fit the CEF excitations and magnetic susceptibility data in powder samples. It is based on two gradient free optimization methods Particle Swarm Optimization (PSO)and Covariance matrix adaptation evolution strategy (CMA-ES)and bypasses the initial step of generating starting values from point-charge model which has proven to be inaccurate at times. In this talk, I will present the results we tested on two reported well-known magnetic lattices, pyrochlore Yb2Ti2O7 [1] and tripod- Er3Mg2Sb3O14 [2]. We found multiple solutions that could fit the data equivalently well and propose to use the local magnetic susceptibility with polarized neutrons to tell the right g-tensor. |
Thursday, March 9, 2023 12:42PM - 12:54PM |
T56.00007: Strong enhancement of magnetic critical temperature followed by loss of magnetism in EuPd3S4 under high pressure shuyuan huyan, Dominic H Ryan, Tyler J Slade, Barbara Lavina, Greeshma C Jose, Haozhe Wang, John M Wilde, Jiyong Zhao, Esen E Alp, Weiwei Xie, Wenli Bi, Sergey L Bud'ko, Paul C Canfield This work presents a comprehensive high-pressure study of the mixed-valent compound EuPd3S4 by electrical transport measurement, 151Eu synchrotron Mössbauer spectroscopy, X-ray absorption spectroscopy, and high-resolution X-ray diffraction. We find that the antiferromagnetic ordering temperature is strongly enhanced from 3 K to 25 K as the pressure is increased to 28 GPa. Above 28 GPa, a clear 1st order Eu2+ to Eu3+ valence transition is observed alongside 1) the vanishing of the magnetic order and 2) a cubic to tetragonal structural phase transition. These rich results suggest that the magnetic ordering temperature is enhanced as 4f hybridization with the conduction band is increased up to a critical value beyond which a sudden valence/ structural transition takes place. As such EuPd3S4 appears to be an excellent system for the detailed study of how magnetism, valence and structure are intertwined and should serve as a benchmark for theoretical efforts to model and understand mixed valence behavior. |
Thursday, March 9, 2023 12:54PM - 1:06PM |
T56.00008: Complex magnetic order and inverse magnetic melting in Ce3TiSb5 Simon M Flury, Marc Janoschek, Wolfgang J Simeth, Yongkang Luo We report high-resolution neutron diffraction on the new heavy fermion material Ce3TiSb5. Ce3TiSb5 exhibits an antiferromagnetic order below TN = 5.5 K. Our specific heat and magnetic susceptibility measurements as a function of magnetic field reveal a phase diagram with three distinct magnetic phases. Using neutron diffraction we study the magnetic structure throughout the phase diagram, and uncover a multi-k spin structure in the intermediate field phase. Magnetic multi-k structures are of current interest because they are an important ingredient for topologically non-trivial properties. Finally, our measurements demonstrate that the high-field magnetic phase exhibits inverse melting, where the magnetically ordered state becomes disordered upon cooling. This is highly unconventional behavior and suggests that the complex magnetic order of Ce3TiSb5 is driven via the competition of several degrees of freedom. |
Thursday, March 9, 2023 1:06PM - 1:18PM |
T56.00009: Antiferromagnetism and field-induced transitions in single crystals of the Remeika phase compound Nd3Rh4Ge13 Samikshya Sahu, Alannah M Hallas Remeika phases with the chemical formula R3T4M13 (R = rare earth, T = transition metal, M = group 14 metals) make up a vast family of intermetallic compounds. This caged structure of the Remeika phase results in a wide range of physical properties, including superconductivity, quantum criticality, and structural distortions, making their characteristics strikingly different for each material. In this talk, we report the first-ever single crystal growth and characterization of Nd3Rh4Ge13 utilizing susceptibility, heat capacity, and electrical transport measurements. Nd3Rh4Ge13 crystallizes in the Yb3Rh4Sn13 cubic structure type and orders antiferromagnetically below TN = 1.6K. In addition, we see evidence of meta-magnetic transitions emerging from the ordered state. We also explore the possibility of iso-valent substitution of rhodium, thereby tuning the spin-orbit coupling (SOC) strength and exchange interactions. These systems allow us to study how the SOC influences the magnetic structures and properties of the rare-earth-based Remeika phases. |
Thursday, March 9, 2023 1:18PM - 1:30PM |
T56.00010: Detecting topological order in Kitaev spin liquids using interpretable machine learning Kevin Zhang, Shi Feng, Yuri D Lensky, Nandini Trivedi, Eun-Ah Kim Much attention has been brought to the rich phase diagram of the honeycomb Kitaev model, which hosts both gapped and gapless Z2 spin liquids in the exactly solvable regime. Here we ask the question: can data-driven techniques be used to discover features governing phase transitions away from the solvable point of the Kitaev model? We approach DMRG ground states from a quantum measurement perspective and take snapshots by repeatedly sampling projective measurements. We train an interpretable neural network architecture, the correlator convolutional neural network [1], to discern characteristic features of different phases [2]. The network is designed to process n-point functions of the spin degrees of freedom, picking out the most relevant terms that can be used to distinguish phases. We finally interpret the correlation functions learned by the neural network and relate them to existing understanding of the studied phases. |
Thursday, March 9, 2023 1:30PM - 1:42PM |
T56.00011: A-site magnetism in quadruple perovskite structure oxides Yuichi Shimakawa, Takashi Saito, Midori Amano Patino, Fabio Denis Romero Quadruple perovskite structure oxides with a chemical formula AA’3B4O12 can accommodate transition-metal ions at both A’ and B sites. When the B site is occupied by non-magnetic cations, the magnetic interactions between the spins at the orthogonally-oriented A’-sites provide a variety of non-trivial magnetic structures in the cubic symmetry sublattices. CaCu3Ge4O12 and CaCu3Sn4O12 show ferromagnetism of the A’-site Cu2+ (S = 1/2) spins due to Cu–Cu direct-exchange interaction, whereas CaCu3Ti4O12 shows the G-type antiferromagnetim, where the antiferromagnetic Cu–O–Ti–O–Cu superexchange interaction overcomes the Cu–Cu direct-exchange interaction. In the solid solution system of CaCu3(Ge-Ti-Sn)4O12, very unusual ferromagnetic-antiferromagnetic-ferromagnetic spin-structure change was observed. In LaMn3V4O12, on the other hands, the nearest neighboring Mn2+ high spins (S = 5/2) align with each other with an angle of 120 degrees. The electrons of V at the B site are delocalized and do not apparently contribute to the magnetic behavior. In CaFe3Ti4O12 and CaCo3Ti4O12 with respectively the A’-site Fe2+ (S = 2) and Co2+ (S = 3/2) spins, the magnetic structures consist of three interpenetrating mutually orthogonal magnetic sublattices. The fourth nearest neighbour spin exchanges as well as spin orbit coupling play an essential role for stabilizing the unusual spin structures. |
Thursday, March 9, 2023 1:42PM - 1:54PM |
T56.00012: Driven Hubbard model on a triangular lattice: Tunable Heisenberg antiferromagnetwith a chiral three-spin term Diptiman Sen We study the effect of a periodically varying electric field on the Hubbard model at half filling on a triangular |
Thursday, March 9, 2023 1:54PM - 2:06PM |
T56.00013: Multi-modal spectroscopy of phase transitions Stephen T Carr, Ilija K Nikolov, Rong Cong, Adrian G Del Maestro, Chandrasekhar Ramanathan, Vesna F Mitrovic To understand a phase transition, independent measurement of the value and variation in each physical parameter of a material's Hamiltonian is vital. Conventional one-dimensional spectroscopy, which studies dynamical responses to fields, struggles to distinguish between different sources of noise. Multi-dimensional spectroscopy can avoid this issue and probe symmetry-specific Hamiltonian parameters by analyzing how the time delay between applied pulses (τ) affects the response. In this work, we present a spectroscopic technique based on the multi-dimensional paradigm which can measure a quadrupolar interaction (inversion symmetric) even in the presence of large magnetic noise (inversion asymmetric). Inversion symmetric combinations of spin operators are found to give clear sinusoidal responses in τ due to periodic refocusing. The time-scale on which the magnetization partially decays in τ provides a direct measure of the distribution of interaction strengths, even when the average value of the interaction is zero. This method independently measures the distributions of different forms of disorder, helping elucidate which microscopic symmetry drives a phase transition. |
Thursday, March 9, 2023 2:06PM - 2:18PM |
T56.00014: Phase Diagram of Compact U(1) gauge theory – a Renormalization Group approach Gautam Nambiar, Jeet Shah, Alexey Gorshkov, Victor M Galitski It was shown by Polyakov that Maxwell theory in 3+1 dimensions can go through a deconfinement – confinement phase transition if the U(1) gauge field is compact. This happens due to a non-perturbative mechanism where monopoles proliferate when the Maxwell coupling exceeds a critical value. In this work, we revisit this phase transition using a renormalization group (RG) approach. The key players in our approach are fields defined on closed strings as opposed to points. We highlight curious aspects of this RG on closed strings that have no analog in conventional field theory. We then explore the phase diagram as a function of the Maxwell coupling and temperature. |
Thursday, March 9, 2023 2:18PM - 2:30PM |
T56.00015: Aharonov-Bohm magnetism in open Fermi surfaces Kostas Vilkelis, Anton Akhmerov, Ady L Stern Orbital diamagnetism requires closed orbits according to the Liftshiftz-Kosevich theory. Therefore, one might expect that open Fermi surfaces do not have a diamagnetic response. Contrary to this expectation, we show that open orbits in finite systems contribute a magnetic response that oscillates between diamagnetism and paramagnetism. The oscillations are similar to the Aharonov-Bohm effect because the oscillation phase is set by the number of flux quanta through the area defined by the width of the sample and the distance between adjacent atomic layers. The magnetic response originates from the closed trajectories formed by counter-propagating open orbits coupled via specular boundary reflections. The phenomenon acts as a probe of the phase coherence of open electron trajectories. |
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