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 L19: Matter in Extreme Environments: Quantum MaterialsFocus Live
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Sponsoring Units: DCOMP DMP Chair: Katerina Hilleke, State Univ of NY - Buffalo |
Wednesday, March 17, 2021 8:00AM - 8:36AM Live |
L19.00001: Pressure induced insulator to metal crossover in van der Waals ferromagnet CrGeTe3 Invited Speaker: Yoshiya Uwatoko The van der Waals material CrGeTe3 has attracted tremendous research interest because of the realisation of Heisenberg type ferromagnetism (FM) in the two-dimensional limit as well as their potential in fabrication of heterostructures with other layered materials. In this work, we have constructed a pressure-temperature electronic phase diagram of CrGeTe3 based on the magnetic susceptibility, χab, resistivity ρab, and Raman spectroscopy data. With increasing pressure up to 11.0 GPa, the ρab decreases by several orders of magnitude, and near a critical pressure Pc ~ 6.5 GPa, ρab displays a correlated Fermi-liquid state which widens with increasing pressure. Below Pc, ρab increases with a -log(T) dependence with decreasing temperature suggesting a 2D weak localization behaviour or Kondo scattering. On the metallic side A-coefficient of T2-term, which represents the electron-electron scattering, diverges on approaching Pc from high pressure side. Furthermore, the χab data reveals that above 3.5 GPa, the long-range FM order disappears and possibly changes either into a short-range type order or a completely different state. The pressure dependence of Raman modes at low temperature clearly suggest deviation of Cr-Te-Cr bonding angle from 90° above 4.0 GPa and rules out any structural transitions in this pressure range. These evidences clearly indicate that the pressure induced insulator to metal transition in CrGeTe3 is driven by electronic correlation without being assisted by structural degree freedom. |
Wednesday, March 17, 2021 8:36AM - 8:48AM Live |
L19.00002: Evolution of Structural, Magnetic and Electronic Properties with Pressure in TMPX3 van-der-Waals Compounds Shiyu Deng, Emilio Artacho, Matthew J Coak, David Jarvis, Hayrullo Hamidov, Cheng Liu, Charles RS Haines, Chris J Pickard, Andrew R Wildes, Siddharth S Saxena Control of dimensionality in condensed matter continues to reveal novel quantum phenomena and effects. TMPX3 (e.g. FePS3) have proven to be ideal examples where structural, magnetic and electronic properties evolve into novel states when their dimensionality is tuned with pressure. At ambient pressure, they are two-dimensional van-der-Waals antiferromagnets, and Mott or charge-transfer insulators. Our recent studies[1-3] have reported dimensionality crossover related pressure-induced insulator-to-metal transitions and novel magnetic phases. There are also reports of superconductivity in a related member of this family of compounds. To further understand the structure and physical property evolution with pressure, we have performed a random structure search using first-principles calculations at high pressures and DFT+U studies to elucidate relationship between structural transitions, magnetism and electronic properties. Our computational explorations into pressure-tuned TMPX3 are expected to guide the discovery of novel phases and superconductivity in these van-der-Waals systems. |
Wednesday, March 17, 2021 8:48AM - 9:24AM Live |
L19.00003: Tuning magnetic and electronic properties in exotic silver(II) fluorides using external pressure and eitaxial strain Invited Speaker: Wojciech Grochala During the last two decades, Ag(II) fluorides have emerged as excellent analogues of undoped Cu(II) oxides. In this account I will illustrate how external pressure may be used to modify crystal structure and properties of these unique low-dimensional antiferromagnets. In addition, role will be discussed of strain for property modification and achieving superconductivity while theoretically modelling the epitaxially grown single layers of AgF2. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L19.00004: Tuning dimensionality, magnetism and conduction in van-der-Waals Mott insulators David Jarvis, Matthew J Coak, Hayrullo Hamidov, Andrew R Wildes, Joseph Paddison, Cheng Liu, Charles RS Haines, Shiyu Deng, Stefan Klotz, Thomas Hansen, Denis P Kozlenko, Je-Geun Park, Siddharth S Saxena We report discovery of new metallic and magnetic phases in the van-der-Waals antiferromagnets MPS3, where M = Transition Metal, form an ideal playground for tuning both low-dimensional magnetic and electronic properties[1-4]. These are layered honeycomb antiferromagnetic Mott insulators, long studied as near-ideal 2D magnetic systems with a rich variety of magnetic and electric properties across the family. |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L19.00005: Neutron Scattering Research on Quantum Materials under Pressure Antonio dos Santos Quantum phenomena exhibits often an extreme sensitivity to weak external perturbations (H, E, P). Among these, pressure is unique in that, even in a moderate range – less than 10 GPa, it induces structural changes that correspond to 1000’s of K, while remaining near the electronic ground state. Also, samples subjected to pressure do not suffer from chemical disorder or impurity phases that may arise from of doping. In this context, neutron scattering, able to inspect both lattice and spin degrees of freedom, while not depositing energy on the sample, is uniquely suitable for the study of quantum systems. Modern neutron sources, such as the SNS, are now coupled with custom made pressure devices that are extend the realm of the possible in terms of exploration of quantum systems with neutrons. Faster measurement on smaller samples are possible across extended ranges of P, T. Here we will present the current suite of instrumentation available to research of quantum materials, including new developments in instrumentation and pressure devices. These advances will be illustrated with science examples that benefited from these new capabilities. |
Wednesday, March 17, 2021 9:48AM - 10:24AM Live |
L19.00006: Hot Hydride Superconductivity above 550 K Invited Speaker: Audrey Grockowiak The search for room temperature (RT) superconductivity (SC) has accelerated dramatically, driven by theoretical predictions that first indicated alloying dense hydrogen with other elements could produce conventional phonon-mediated SC at very high temperatures and at accessible pressures, and then with the success of structure search methods that have identified specific candidates and pressure-temperature (P-T) conditions for synthesis. As a result, experimental studies of simple binary hydrides under pressure have yielded high critical SC transition temperatures (Tc), of 260K in LaH10, close to RT, at pressures near 180GPa. We successfully synthesized a metallic La based superhydride from La metal and NH3BH3, and find an initial multi-step transition with a Tc of 294K for the highest onset, in line with previous work[1],[2]. Subsequent thermal excursions to higher temperatures promoted a chemical reaction a ternary or higher order system, confirmed by X-ray diffraction. Although the reaction does not appear to be complete, the onset temperature was pushed from 294K to 556K. The results provide evidence for hot superconductivity well above RT, in line with recent predictions for a higher order hydride under P[3]. |
Wednesday, March 17, 2021 10:24AM - 10:36AM Live |
L19.00007: Theoretical Predictions of Ternary Hydrides Under Pressure Nisha Geng, Xiaoyu Wang, Tiange Bi, Morgan Redington, Eva Zurek It has been found that hydrogen-rich materials are good candidates for superconductivity under pressure. Inspired by the discovery of high temperature superconductivity in binary hydrides of sulphur and calcium, we considered a number of ternary systems containing these elements. The XtalOpt evolutionary algorithm was used to predict their crystal structures, and first-principles calculations were carried out to determine the properties, bonding and electronic structures of stable and metastable structures. A number of superconducting phases have been found with critical temperatures ranging between 60 K to 120 K. |
Wednesday, March 17, 2021 10:36AM - 10:48AM Live |
L19.00008: High-pressure phase diagram of ferromagnetic superconductor Eu(Fe0.75Ru0.75)2As2 Zachary Nix, Jiyong Zhao, Esen Alp, Michael Y. Hu, Guang-Han Cao, Wenli Bi Eu(Fe0.75Ru0.75)2As2 is an intriguing system with unusual coexistence of superconductivity (TC ~23 K) and ferromagnetism (Tm ~ 20 K) and provide a unique platform to study of the nature of such coexistence. To establish a microscopic magnetic phase diagram of the recent doped 122-type ferromagnetic superconductor Eu(Fe0.75Ru0.75)2As2, time-resolved synchrotron Mössbauer experiments 151Eu have been performed on a single crystalline sample under hydrostatic pressures and low temperatures. Under compression, the magnetic ordering temperature first increase sharply from 22 K at ambient pressure to 53 K at 10 GPa. With further compression, the magnetic ordering temperature decreases and the magnetic order is fully suppressed above 25.2 GPa. Evolution of the magnetic state with pressure will be discussed in detail. |
Wednesday, March 17, 2021 10:48AM - 11:00AM Live |
L19.00009: Superconductivity in elemental yttrium and yttrium superhydride bulk and film at high pressures Jonathan Buhot, Owen Moulding, Takaki Muramatsu, Israel Osmond, Sam Cross, Oliver Lord, Sven Friedemann The quest for room temperature superconductivity has always been one of the most intense topics in condensed matter physics. It has reached its peak with the recent discovery of several superhydride compounds exhibiting superconductivity at vicinity of room temperature under megabars pressures, such as YH9. While theoretical works are paving the way to realize new hydrides superconductors, their synthesis within the laboratory remains very challenging. Here we demonstrate a new approach to synthesize YHx from an elemental yttrium film directly evaporated on the diamond anvil [1]. This method allows a more accurate control of the sample size and helps to reach an ideal stoichiometry in the synthesis. Our measurements show that electronic properties of elemental yttrium bulk and film are similar. Superconducting temperatures we measure in elemental yttrium under megabar pressures together with a re-analyse of previous x-ray data provide evidence of the predicted Fddd phase above 100 GPa. Furthermore, we will show that it is possible to synthetize an yttrium superhydride superconductor film. |
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