Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V52: Magnetic Topological Materials 7: New MaterialsLive
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Sponsoring Units: DMP GMAG Chair: Weiwei Xie, Rutgers, The State University of New Jersey |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V52.00001: Ultrafast carrier dynamics in the ferromagnetic semimetal EuCd2As2 Ken ONeal, Prashant Padmanabhan, La Moyne Mix, Min Cheol Lee, Nicholas Sirica, Brinda Kuthanazhi, Sergey L. Bud'ko, Paul C Canfield, Rohit P Prasankumar, Dmitry Yarotski We report the near-infrared pump-probe ultrafast response of the ferromagnetic candidate Weyl semimetal EuCd2As2. A non-pulsewidth limited rise dynamic is followed by two distinct decay processes – a sub-picosecond decay attributed to electron-phonon relaxation and a several picosecond long process which stems from demagnetization of the in-plane magnetic moment. Exponential fits of the decay processes down to 6 K reveal subtle sensitivity to the long-range magnetic ordering. Surprisingly, the strongest effects take place near 80 K despite negligible changes in ARPES. Time-resolved magneto-optical Kerr effect measurements will provide further insight into this critical temperature scale. |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V52.00002: Broken-helix antiferromagnetic order protecting a crystalline axion insulator phase and exotic surface states in EuIn2As2 Simon Riberolles, Thais Victa Trevisan, Brinda Kuthanazhi, Thomas W Heitmann, Feng Ye, David C Johnston, Sergey L. Bud'ko, Dominic H Ryan, Paul C. Canfield, Andreas Kreyssig, Ashvin Vishwanath, Robert J McQueeney, Lin-Lin Wang, Peter Orth, Benjamin Ueland EuIn2As2 is theoretically predicted to order in a collinear antiferromagnetic structure that preserves inversion symmetry and induces an axion-insulator state. Combining results from neutron diffraction, symmetry analyses and density functional theory, we show that EuIn2As2 instead exhibits low-symmetry helical antiferromagnetic order which breaks inversion. However, the combination of a 180° rotation and time-reversal symmetry (C2 x T= 2’) elements still makes the compound a stoichiometric magnetic topological-crystalline axion insulator. Surfaces normal to the 2' symmetry axes show exotic gapless Dirac cones (DC) which are unpinned to specific time-reversal invariant momenta (TRIM). Gapped DC pinned to TRIM appear on the other surfaces. Dissipationless charge transport arises on the 2' protected surfaces while half-integer quantum anomalous-type conductivity occurs on the other surfaces. We predict that modest values of applied magnetic field can switch between the different surfaces states. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V52.00003: Anomalous Quantum oscillations of magnetic topological semimetal EuCd2Sb2 Yue Shi, Qianni Jiang, Zhaoyu Liu, Jiun-Haw Chu Magnetic topological material is an ideal platform to explore the interplay between magnetism and electronic structures. In this talk, I will present the quantum oscillations study of an antiferromagnetic topological insulator EuCd2Sb2, which was proposed to be a magnetic Weyl semimetal in the field-induced ferromagnetic state. By comparing with the nonmagnetic analogue SrCd2Sb2, we discovered shifts of the peak and valley positions of quantum oscillations of EuCd2Sb2 as the temperature increases. We argued that this anomalous behavior is a consequence of the change of band structure due to the decrease of Eu magnetization. |
Thursday, March 18, 2021 3:36PM - 3:48PM Live |
V52.00004: Solution growth and physical properties of RPd3S4 topological semimetals Tyler Slade, Lin-Lin Wang, Sergey Budko, Paul C. Canfield Topological materials feature unique electronic structures marked by symmetry protected states that give rise to remarkable properties including high magnetoresistance and anomalous Hall effect. We present a study of the sulfide bronzes RPd3S4 (R = rare earth), which adopt the cubic Pm-3n structure. The nonmagnetic Y and La members are predicted to host Dirac and other symmetry protected high degeneracy points in their electronic structures, and the moment bearing analogues exhibit both ferro- and antiferromagetic order, indicating RPd3S4 may represent a new family of magnetic TSMs. We provide a solution growth of mm-sized RPd3S4 for R = La, Ce, Nd crystals. Our synthesis utilizes the Pd-S eutectic and fritted crucibles that allow for re-use and fractionation of reaction melts to determine the optimal conditions for crystallization. We anticipate the methodology to be generalizable to other materials with difficult crystal growths. Finally, we present characterization of the magnetic and electronic transport properties of our RPd3S4 crystals. |
Thursday, March 18, 2021 3:48PM - 4:00PM Live |
V52.00005: Experimental electronic structure of the electronically switchable antiferromagnet, CuMnAs Andrew Linn, Kyle Gordon, PEIPEI HAO, Dushyant Narayan, Bryan Berggren, Nathaniel Allen Speiser, Sonka Reimers, Libor Smejkal, Thomas Jungwirth, Jonathan Denlinger, Peter Wadley, Daniel Dessau Tetragonal CuMnAs is a room temperature antiferromagnet with an electrically reorientable Néel vector. We report direct measurements of the electronic structure of single-crystalline thin films using ARPES. We extract Fermi surfaces (FS) and E-k dispersions. After correcting for an unexpected chemical potential shift of -430 meV (hole doping), we find excellent agreement of FS, orbital character, and Fermi velocities between experiment and Density Functional Theory calculations (DFT), using GGA+U with U = 3 eV. We also find 2x1 surface reconstructions in LEED and ARPES. This work underscores the need to control the chemical potential in tetragonal CuMnAs to enable the exploration and exploitation of the topological quantum switching of the Dirac point above the chemical potential in the current samples. |
Thursday, March 18, 2021 4:00PM - 4:12PM Live |
V52.00006: Topological Descendants of Multicritical EuTl2 Lin-Lin Wang, Hoi Chun Po, Robert-Jan Slager, Ashvin Vishwanath Aided by a refined understanding of topological band structures with crystalline symmetries that has emerged recently, many electronic phases have been identified and a plethora of materials have been predicted to host novel properties and functionalities. Here we describe a paradigmatic semimetal that simultaneously incorporates multiple, and sometimes conflicting topology which guarantees gaplessness and leads to an exceptionally rich family of descendent phases on lowering symmetry. We predict that this multicritical phase is realized in EuTl2. Starting from the parent semimetallic state, which already separates two topological insulating regimes, the interplay of inherent magnetism and strain allows for an exceptionally rich phase diagram of topological descendant states. |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V52.00007: Exploring broken time-reversal symmetry in Cd3As2/(Ga,Mn)Sb Dirac semimetal/ferromagnetic semiconductor heterostructures Arpita Mitra, Run Xiao, Alexander Grutter, Julie Borchers, Brian Kirby, Patrick Quarterman, NITIN SAMARTH Cd3As2 has attracted attention as a canonical Dirac semimetal. We aim to break time reversal symmetry (TRS) in Cd3As2 by interfacing with a ferromagnetic semiconductor (Ga,Mn)Sb.We have grown epitaxial Cd3As2 /(Ga,Mn)Sb bilayers by molecular beam epitaxy on GaSb(111) buffer layer using GaAs(111)B substrates.High-resolution XRD shows good crystalline quality of Cd3As2 layers with full width half maximum of rocking curves ~0.11°.AFM shows smooth surface of Cd3As2 with root mean square roughness ~1.2 nm.SQUID magnetometry reveals weak ferromagnetism in (Ga,Mn)Sb films,while low temperature magnetoresistance (MR) data show that they are highly resistive for the Mn composition used.We report the temperature dependent magneto-transport properties in Cd3As2/(Ga,Mn)Sb bilayers and investigate the magnetic proximity effect at the interface.The observation of hysteretic MR and a planar Hall effect suggest proximity-induced ferromagnetic ordering in Cd3As2.We have performed polarised neutron reflectivity measurements to get an indication of the proximity effect at the interface.We are exploring interfacing Cd3As2 with other ferromagnetic insulators in order to find an efficient material for breaking TRS in Cd3As2. |
Thursday, March 18, 2021 4:24PM - 4:36PM Not Participating |
V52.00008: Investigation into the Eu Based 122 Family of Magnetic Topological Candidates Madalynn Marshall, Ivo Pletikosić, Tay-Rong Chang, Huibo Cao, Weiwei Xie Incorporating additional quantum phases such as magnetism into topological materials can open the door to new and advanced quantum technology. This research highlights the new intrinsic magnetic topological quantum material candidate, EuMg2Bi2. Magnetic susceptibility measurements performed by ORNL indicate that EuMg2Bi2 orders antiferromagnetically at TN = 8.2 K. To further investigate the electronic behavior, ARPES data was performed in collaboration with Brookhaven National Laboratory (BNL) and confirmed the surface state of EuMg2Bi2 to be similar to the observed type II nodal line semimetal Mg3Bi2 previously determined in our group. Recently, neutron scattering measurements revealed EuMg2Bi2 to exhibit an A-type magnetic structure, which is consistent with the work reported here. In order to gain further insight into the potential coupling between the magnetism and topological states, the magnetic behavior and topology was considered for multiple materials related to EuMg2Bi2. From this research an in-depth discussion of the magnetic behavior, design and prediction of Eu based 122 materials has been realized. |
Thursday, March 18, 2021 4:36PM - 4:48PM Live |
V52.00009: Linear and Nonlinear Optical Spectroscopy Studies of a Magnetic Weyl Semimetal Co3Sn2S2 Youngjun Ahn, Rachel Owen, Elizabeth Drueke, Kejian Qu, Rui Xue, David George Mandrus, Liuyan Zhao Co3Sn2S2 has received immense popularity in the condensed matter physics community because it is both a promising candidate for a magnetic Weyl semimetal and a non-Bravais Kagome lattice ferromagnet. So far, a careful correlation between the surface and the bulk properties, including structural, magnetic, and electronic properties, has yet to be explored comprehensively. In this talk, we will present our selective studies of the surface and bulk properties by conducting optical rotational anisotropy experiments of second and third harmonic generations (S/THG), respectively, using near-infrared wavelength light. We will also use light polarization to distinguish between the magnetic and the structural/electronic contributions in both linear and nonlinear S/THG optical measurements. Finally, we will carefully track the temperature dependence of both the linear and nonlinear optical responses across the magnetic critical transition temperature. |
Thursday, March 18, 2021 4:48PM - 5:00PM Live |
V52.00010: Time- and angle-resolved photoemission spectroscopy of the intrinsic antiferromagnetic topological insulator EuSn2P2 Nina Bielinski, Soyeun Kim, Mebatsion Gebre, Daniel Shoemaker, Fahad Mahmood EuSn2P2 was recently predicted to be an antiferromagnetic topological insulator below TN = 30 K. This makes it an ideal candidate to explore the interplay between magnetism and topology including axion electrodynamics. Here we use time- and angle- resolved photoemission spectroscopy (tr-ARPES) to observe and characterize the Dirac surface states of EuSn2P2 both above and below TN. An IR pump pulse populates the previously unoccupied surface states near the Dirac point and a time delayed probe pulse measures the transient ARPES spectra. We will discuss changes in the tr-ARPES decay dynamics across the magnetic transition and further understand the topological nature of the bands using circular dichroism ARPES. |
Thursday, March 18, 2021 5:00PM - 5:12PM Live |
V52.00011: Magnetic sturcutre of an intrinsic magnetic topological insulator, EuSn2As2, probed via X-ray resonant exchange scattering Zahir Islam, Ulrich Welp, Duck Young Chung, Wai-Kwong Kwok, Mercouri Kanatzidis Intrinsic magnetic topological insulators devoid of defects and disorder which can be detrimental to topological quantum phenomena are of interest. Since magnetism breaks time reversal symmetry and allows to tune the system's spatial symmetry thereby opening a way to induce exotic phenomena such as axion states. In this work, we used high-resolution resonant X-ray scattering to study magnetic long-range order in the recently discovered topological material EuSn2As2. In this rhombohedral system an antiferromagnetic (AFM) transition is observed below 25 K. Our diffraction studies revealed a long-range three dimensionally ordered magnetic phase with an ordering vector, q=(0,0,1/2), indicating a 2-unit-cell magnetic periodicity along the c axis in hexagonal notation and consisting of ferromagnetic Eu-layers stacked in an antiferromagnetic fashion. Order parameter data indicates a TN of 24.1K. |
Thursday, March 18, 2021 5:12PM - 5:24PM Live |
V52.00012: Structural and physical properties of topological semimetal candidate EuZn2As2 Joanna Blawat, Madalynn Marshall, Huibo Cao, Weiwei Xie, Rongying Jin Recent theoretical calculations predict nontrivial topology in magnetic materials, such as EuCd2As2, with the type-IV magnetic space group symmetry. We have successfully grown EuZn2As2 single crystals with the trigonal structure (P-3m1) as determined by the X-ray diffraction measurements. The magnetic susceptibility, electrical resistivity, and specific heat indicate that EuZn2As2 orders antiferromagnetically (AFM) at TN = 19 K. Single crystal neutron diffraction refinement reveals the A-type AFM structure of Eu with the ordered moment of 7.33μB. At T < TN, the (0 0 ½) peak intensity increases and can be described by (TN – T/TN)2β with β ~ 0.23, implying two-dimensional magnetic ordering. These results indicate that EuZn2As2 exhibits the same crystallographic and magnetic structure as that of EuCd2As2. |
Thursday, March 18, 2021 5:24PM - 5:36PM Live |
V52.00013: Magnetic order in the Dirac material EuMnSb2 John Wilde, Benjamin Ueland, Simon Riberolles, Dominic H Ryan, Andreas Kreyssig, David Vaknin, Thomas W Heitmann, Yong Liu, Sergey Budko, Robert J McQueeney EuMnSb2 is a potential Dirac semimetal with Dirac fermions located within the Sb layers. Here we present results from single-crystal neutron diffraction experiments on EuMnSb2. We find that the Eu and Mn magnetic sublattices order antiferromagnetically (AF) below 24(1) K and 324(1) K, respectively, with an additional magnetic phase transition at 9(1) K which may be related to the coupling between both magnetic sublattices. Neutron diffraction shows that each AF phase is characterized by a magnetic unit cell equal to the chemical one. |
Thursday, March 18, 2021 5:36PM - 5:48PM Live |
V52.00014: Onset of non-linear IV transport with magnetic order in a Mott insulator Tanya Berry, Dominic H Ryan, Raivo Stern, Nitesh Kumar, Nicodemos Varnava, Veronica Stewart, Walter Schnelle, Rishi Banda, Vincent Charles Morano, Defa Lui, Qingge Mu, Lakshmi Bhaskaran, Christopher Pasco, Mazhar Ali, Norman Armitage, Collin Leslie Broholm, Claudia Felser, David Vanderbilt, Tyrel McQueen We observe a non-linear voltage and current relation in the layered magnetic semiconductor EuMn2P2 when it approaches its ordering temperature. Such behavior is seen in materials that have charge density wave order, or those proximal to metal-insulator transitions such as the current switching of resistive states in magnetoresistive manganites. However, none of the preceding occurs in EuMn2P2. We observe a spin-order driven magnetic transport in the voltage and current relation. Our results in this work could reveal some unanswered questions of conduction and spins in the Mott Insulator model. We suggest that such phenomena could be exploited in non-linear antiferromagnetic insulators and we also provide a route to observing such behavior using chemical design principles. |
Thursday, March 18, 2021 5:48PM - 6:00PM Live |
V52.00015: Magnetic generation and switching of topological quantum phases in a trivial semimetal α-EuP3 Alex Mayo, Hidefumi Takahashi, Mohammad Saeed Bahramy, Atsuro Nomoto, Hideaki Sakai, Shintaro Ishiwata Black phosphorus (BP), a material consisting of monoatomic phosphorene layers stacked via van der Waals bonding, is a narrow-gap semiconductor in ambient pressure. It has recently been predicted that BP undergoes a topological transition by applying high pressure, resulting in a semi-metallic band structure. α-EuP3 has a crystal structure closely related to BP and contains magnetic Eu2+ ions between the P layers. Recent first principle calculations predict that semi-metallic band structures originating mainly from the p-orbital of phosphorus are realized in α-SrP3, which is an isostructural crystal of α-EuP3. Therefore, in α-EuP3 we expect the emergence of non-trivial electronic transport derived from the correlation between magnetism and the semi-metallic electronic structure. So far, we have observed the anomalous Hall effect, which abruptly emerges at a certain value of magnetization. This suggests that the magnetically tuned band structure plays an important role. In this presentation, we will discuss the correlation between the exchange splitting and the electronic transport properties, and also the possibility of a topological origin of the anomaly. |
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