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Research Focus
Correlations among electrons in metals lead to a variety of different phases, including superconductivity, magnetic and charge ordering, topological phases such as the fractional quantum Hall effect, and even whether those electrons are free to move or become localized, bearing a magnetic moment. The relationships among these different phases of matter are complex, and as new materials are discovered we gain better understanding of the scope of phase behaviors that are possible, and by studying their relative stabilities we can learn how they are related. Of special interest is the physics found near T=0 phase transitions, also known as quantum critical points (QCPs).
The long-term objective of our research is to understand what stabilizes T=0 collective phases in electronic systems with strong correlations, and how they are connected at QCPs. We seek to extend our understanding in two ways:
· It is increasingly appreciated that the nature of T=0 phase transitions and the associated T=0 phases result from more than broken symmetries, which involve the spatial arrangements of atoms and moments. Some systems have no broken symmetries, but differ in their global properties, characterized by topological invariants such as the Chern number of electronic bands, or the global flux of an emerging gauge field. Are the instabilities and phase transitions of these topological systems distinct from the interaction-driven QCPs? What new phases may emerge?
· There is a need to extend our understanding to new types of magnetic systems with T=0 instabilities. In particular, one dimensional systems are rich in T=0 phases, which are readily frustrated by strong quantum fluctuations. While the theoretical context for one-dimensional magnetism is well developed for insulators, at present a lack of metallic spin chain materials prevents their integration in generic phase diagrams. What new phases might emerge in spin chains with strong electronic correlations? Does the transition from localized to delocalized magnetism proceed differently in 1D and 3D?
Our experimental program is driven by the discovery and development of new metallic systems that exemplify different aspects of quantum criticality and order. We synthesize the high quality single crystals using both flux growth and liquid and vapor transport techniques. Our experimental approach is centered on neutron scattering measurements that assess the spatial and dynamical correlations that occur near phase transition. They are carried out at user facilities in Europe, Japan, and the US. Complementary investigations of the magnetic, thermal, and transport properties are carried out in our laboratory, and in collaboration with other groups in the SBQMI.
Current Projects
At present, we are working on two different projects that explore different aspects of quantum criticality.
Phase diagrams for the S=1/2 Frustrated exchange model with competing 1st and 2d neighbor exchange J1/J2 and XXZ anisotropy. Ti4MnBi2 forms very near the intersection of FM,AF, and chiral phases.
Phase diagrams for the S=1/2 Frustrated exchange model with competing 1st and 2d neighbor exchange J1/J2 and XXZ anisotropy. Ti4MnBi2 forms very near the intersection of FM,AF, and chiral phases.
I.Topological phases and their instabilities in correlated metals.
We have shown that the series LaSbxTe2-x (0.8<x<1) (LST) is an ideal platform for exploring a topological phase transition, a key advance that will allow us to explore and exploit fundamental phenomena, with an eye towards their potential applicability for future quantum technologies. Current work centers on establishing the existence of topological QCPs that lead to the collapse of the Weyl fermions and the emergence of new types of order. Of particular interest is clarifying the role of electronic correlations, especially leading to magnetism and superconductivity.
“Electronically driven switching of topology in LaSbTe”, J. Bannies, M. Michiardi, H. -H. Kung, S. Godin, J. W. Simonson, M. Oudah, M. Zonno, S. Gorovikov, S. Zhdanovich, I. S. Elfimov, A. Damascelli, and M. C. Aronson (arXiv:2407.08798)
``Time-Reversal Symmetry Breaking Superconductivity in CaSb2’’, M. Oudah, Y. Cai, M. V. De Toro Sanchez, J. Bannies, M. C. Aronson, K. M. Kojima, D. A. Bonn, Physical Review B 110, 134524 (2024).
``Superconductivity and Quantum Oscillations in Single Crystals of the Compensated Semimetal CaSb2'', M. Oudah, J. Bannies, D. A. Bonn, and M. C. Aronson, Physical Review B 105, 184504 (2022).
II.Quantum fluctuations and phases in one dimensional metals and magnets.
1D physics has played a central role in our understanding of quantum fluctuations, due to an unusually close synergy among minimal Hamiltonians, powerful theoretical tools, and the robustness of the 1D character of real materials that permits the close comparison of theoretical and experimental results over a broad range of energies and temperatures. At present, much of what we know about magnetic 1D systems instead comes from compounds that are insulating due to strong correlations, and so we currently have little access to the broader class of excitations and instabilities that may be expected in 1D correlated electron systems. Our group has pursued a targeted search for metallic spin chains that led to a discovery of the only known examples, Yb2Pt2Pb and Ti4MnBi2. Inelastic neutron scattering measurements, combined with DMRG calculations, show that Ti4MnBi2 is well described as a spin ½ chain with competing near neighbor and next nearest neighbor exchange interactions. It forms out of a T=0 antiferromagnetic phase, with helical modulation. However, strong quantum fluctuations prohibit true long-ranged order, as expected for a one-dimensional system.
``Frustrated S = 1/2 Chains in One-Dimensional Correlated Metal Ti4MnBi2’’ , X. Y. Li, A. Nocera, K. Foyevtsova, G. A. Sawatzky, M. Oudah, N. Murai, M. Kofu, M. Matsuura, H. Tamatsukuri, M. C. Aronson (arXiv:2409.02880 )
``Correlations and incipient antiferromagnetic order within the linear Mn chains of metallic Ti4MnBi2'' A. Pandey, P. Miao, M. Klemm, H. He, M. Green, Z. Xu, Y. Zhao, X. Qian, J. W. Lynn, and M. C. Aronson, Phys. Rev. B 102, 014406 (2020).
``Spinon confinement and a sharp longitudinal mode in Yb2Pt2Pb in magnetic fields'', W. J. Gannon, I. A. Zaliznyak, L. S. Wu, A. E. Feiguin, A. M. Tsvelik, F. Demmel, Y. Qiu, J. R. D. Copley, M. S. Kim & M. C. Aronson, Nature Communications 10, Article number: 1123 (2019).
``Orbital-Exchange and fractional quantum number excitations in an f-electron metal Yb2Pt2Pb’’, L. S. Wu, W. J. Gannon, I. A. Zaliznyak, A. M. Tsvelik, M. Brockmann, J.-S. Caux, M. -S. Kim, Y. Qiu, J. R. Copley, G. Ehlers, A. Podlesnyak, and M. C. Aronson, Science 352, 1206 (2016).
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