Spin-Orbit Coupling and Topological Systems

Phase transitions in condensed matter physics generally have been identified with an order parameter that spontaneously breaks the symmetry of the system and develops long range order, such as for the magnetization that develops in a ferromagnet below the Curie temperature or the staggered magnetization below the Néel temperature in an antiferromagnet.  With the discovery of the Integer Quantum Hall Effect, and now for Topological Insulators (TI), the traditional classification of quantum phases of matter has expanded.  These latter systems lack the concept of spontaneous symmetry breaking, rather exhibiting topological order associated with the presence of nontrivial topological components that lead to gapless boundary modes with chirality. One of the essential properties of TI's is a strong spin-orbit interaction, which interaction becomes larger the heavier the element.  For the well-studied 3d systems the spin-order interaction typically does not play an essential role, which is one of the reasons attention in the condensed matter community has turned to 4d, 5d, and 5f systems. 

Further expansion of these new and fascinating systems now includes Topological Semimetals.  In the Weyl semimetal CeAlGe, Joe Checkelsky's group at M.I.T. has discovered the particularly interesting phenomenon of Singular Angular MagnetoResistance (SAMR).  For a general explanation please see the news item at https://news.mit.edu/2019/approaching-magnetic-singularity-0620, while the publication can be found at  Science 365, 377 (2019);  (perspectivve by Hassinger and Meng).

Half-Heusler Topological Insulators and Related

In the so-called Z₂ two-dimensional and three-dimensional systems, these topologically protected metallic states are of interest not only from a fundamental point of view, but also because they have the technological potential to transform spintronics and quantum computation applications. Even more interesting are systems that exhibit both symmetry breaking order parameters and topologically nontrivial states, which can give rise to exotic collective modes and states.  One such family is represented by the cubic half-Heusler materials on which we have been collaborating.  The antiferromagnetism breaks time reversal and translational symmetries but preserves the combination, leading to a new type of system, the antiferromagnetic topological insulator.

Topological RPdBi half-Heusler semimetals:  a new family of non-centrosymmetric magnetic superconductors, Y. Nakajima, R. Hu, K. Kirshenbaum, A. Hughes, P. Syers, X. Wang, K. Wang, R. Wang, S. Saha, D. Pratt, J.W. Lynn, and J. Paglione, Science Advances 1, e1500242 (2015).

Large Anomalous Hall Effect in a Half Heusler Antiferromagnet, T. Suzuki, R. Chisnell, A. Devarakonda, Y.-T. Liu, J. W. Lynn, and J. G. Checkelsky, Nature Physics 12, 1119 (2016).  Press Release.

Carrier Density Control of Magnetism and Berry Phases in Doped EuTiO₃, Kaveh Ahadi, Zhigang Gui, Zach Porter, Jeffrey W. Lynn, Zhijun Xu, Stephen D. Wilson, Anderson Janotti, and Susanne Stemmer,, APL Materials 6, 056105 (2018).

Amplitude Mode in a Classical, Two-dimensional Triangular Antiferromagnet, Rebecca L. Dally, Yang Zhao, Zhijun Xu, Robin Chisnell,  Matthew Stone, Jeffrey W. Lynn, Leon Balents, and Stephen D. Wilson, Nature Communications 9, 2188 (2018).

Singular Angular Magnetoresistance and Spontaneous Symmetry Breaking in a Magnetic Nodal Semimetal, T. Suzuki, L. Savary, J.-P. Liu, J. W. Lynn, L. Balents, and J. G. Checkelsky, Science (2019).  Press Release.

5d sytems;  Iridates

Discovery of Topological Singularity Induced Kohn Anomaly in Weyl Semimetal, Thanh Nguyen, Fei Han, Nina Andrejevic, Ricardo Pablo-Pedro, Anuj Apte, Zhiwei Ding, Kunyan Zhang, Ahmet Alatas, Ercan Alp, Songxue Chi, Jaime Fernandez-Baca, Masaaki Matsuda, David A. Tennant, Yang Zhao, Zhijun Xu, Jeffrey W. Lynn, Shengxi Huang, and Mingda Li, (submitted), arXiv:1906.00539.

Influence of Electron-doping on the Ground State of (Sr_1-xLa_x)₂IrO₄, Xiang Chen, Tom Hogan, D. Walkup, Wenwen Zhou, M. Pokharel, Mengliang Yao, Wei Tian, Thomas Z. Ward, Y. Zhao, D. Parshall, C. Opeil, J. W. Lynn, Vidya Madhavan, and Stephen D. Wilson, Phys. Rev. B 92, 017125 (2015).

Carrier Localization and Electronic Phase Separation in a doped Spin-Orbit Driven Mott Phase in Sr₃(Ir_1-xRu_x)₂O₇, Chetan Dhital, Tom Hogan, Wenwen Zhou, Xiang Chen, Zhensong Ren, Mani Pokharel, Yoshinori Okada, M. Heine, Wei Tian, Z. Yamani, C. Opeil, J. S. Helton, J. W. Lynn, Ziqiang Wang, Vidya Madhavan, and Stephen D. Wilson, Nature Communications 5, 3377 (2014).

Cd-doping effects in Ce₂MIn₈ (M=Rh and Ir) Heavy Fermion Compounds, C. Adriano, C. Giles, E. M. Bitter, L. N. Coelho, F. de Bergevin, C. Mazzoll, L. Paolasini, W. Ratcliff, R. Bindel, J. W. Lynn, Z. Fisk, and P. G. Pagliuso, Phys. Rev. B 81, 245115 (2010).

Novel Coexistence of Superconductivity with Two Distinct Magnetic Orders in Heavy Fermion Ce(Rh,Ir)In₅, A. D. Christianson, A. Llobet, W. Bao, J. S. Gardner, I. P. Swainson, J. W. Lynn, J.-M. Mignot, K. Prokes, P. G. Pagliuso, N. O. Moreno, J. L. Sarrao, and A. H. Lacerda, Phys. Rev. Lett. 95, 217002 (2005).

Covalency Effects in the Magnetic Form Factor of Ir in K₂IrCl₆, J. W. Lynn, G. Shirane, and M. Blume, Phys. Rev. Lett. 37, 154 (1976).

4d materials;  Ruthenates

Phase Diagram of a-RuCl₃ in an in-plane Magnetic Field, J. A. Sears, Y. Zhao, Z. Xu, J. W. Lynn, and Young-June Kim, Phys. Rev. B 95, 180411(R) (2017).

Spin Dynamics and Two-dimensional Correlations in an FCC Antiferromagnetic Sr₂YRuO₆, S. M. Disseler, J. W. Lynn, R. F. Jardim, M. S. Torikachvili, and E. Granado, Phys. Rev. B 93, 140407(R) (2016).

Two-Dimensional Magnetic Correlations and Partial Long-Range Order in Geometrically Frustrated Sr₂YRuO₆, E. Granado, J. W. Lynn, R. F. Jardim, and M. Torikachvili, Phys. Rev. Lett. 110, 017202 (2013).

Spin-valve Effect and Magnetoresistivity in Single Crystalline Ca₃Ru₂O₇, W. Bao, Z. Q. Mao, Z. Qu, and J. W. Lynn, Phys. Rev. Lett. 100, 247203 (2008).

Unusual heavy-mass nearly ferromagnetic state with a surprisingly large Wilson ratio in double layered ruthenates (Sr_1-xCa_x)₃Ru₂O₇, Z. Qu, L. Spinu, H. Q. Yuan, V. Dobrosavljeviuc, W. Bao, J. W. Lynn, M. Nicklas, J. Peng, T. J. Liu, D. Fobes, E. Flesch, and Z. Q. Mao, Phys. Rev. B 78, 180407(R) (2008).

Structure and Magnetism of Single Crystal Sr₄Ru₃O₁₀:  A Ferromagnetic Triple-Layer Ruthenate, M. K. Crawford, R. L. Harlow, W. Marshall, Z. Li, G. Cao, R. L. Lindstrom, Q. Huang, and J. W. Lynn, Phys. Rev. B 65, 214412 (2002).

Synthesis and crystal structure of La₃RuO₇, P. Khalifah, Q. Huang, J. W. Lynn, R. W. Erwin, and R. J. Cava, Materials Research Bulletin 35, 1 (2000).

Oxygen Displacements and Search for Magnetic Order in Sr₃Ru₂O₇, Q. Huang, J. W. Lynn, R. W. Erwin, J. Jarupatrakorn, and R. J. Cava, Phys. Rev. B 58, 8515 (1998).

5f materials;  Hidden order in URu₂Si₂

High temperature singlet-based magnetism from Hund's rule correlations, Lin Miao, Rourav Basak, Sheng Ran, Yishuai Xu, Haowei He, Jonathan D. Denlinger, Yi-De Chuang, Y. Zhao, Z. Xu, J. W. Lynn, J. R. Jeffries, S. R. Saha, Ioannis Giannakis, Pegor Aynajian, Chang-Jong Kang, Yilin Wang, Gabriel Kotliar, Nicholas P. Butch, L. Andrew Wray, (submitted).

Distinct magnetic spectra in the hidden order and antiferromagnetic phases in URu_2-xFe_xSi₂, Nicholas P. Butch, Sheng Ran,

Inho Jeon, Noravee Kanchanavatee, Kevin Huang, Alexander Breindel, M. Brian Maple, Ryan L. Stillwell, Yang Zhao, Leland Harriger, and Jeffrey W. Lynn, Phys. Rev. B 94, 201102 (2016).

Chemical Pressure Tuning of URu₂Si₂ via Isoelectronic Substitution of Ru with Fe, Pinaki Das, N. Kanchanavatee, J. S. Helton, K. Huang, R. E. Baumbach, E. D. Bauer, B. D. White, V. W. Burnett, M. B. Maple, J.W. Lynn, and M. Janoschek, Phys. Rev. B 91, 085122 (2015).

Symmetry and Correlations Underlying Hidden Order in URu₂Si₂, Nicholas P. Butch, Michael E. Manley, Jason R. Jeffries, Marc Janoschek, Kevin Huang, M. Brian Maple, Ayman H. Said, Bogdan M. Leu, and Jeffrey W. Lynn, Phys. Rev. B 91, 035128 (2015).

Antiferromagnetic Critical Pressure in URu₂Si₂ under Hydrostatic Conditions, N. P. Butch, J. R. Jeffries, S. X. Chi, J. B. Leão, and J. W. Lynn, and M. B. Maple, Phys. Rev. B 82, 060408(R) (2010).

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