1
|
Hong T, Ying T, Huang Q, Dissanayake SE, Qiu Y, Turnbull MM, Podlesnyak AA, Wu Y, Cao H, Liu Y, Umehara I, Gouchi J, Uwatoko Y, Matsuda M, Tennant DA, Chern GW, Schmidt KP, Wessel S. Evidence for pressure induced unconventional quantum criticality in the coupled spin ladder antiferromagnet C 9H 18N 2CuBr 4. Nat Commun 2022; 13:3073. [PMID: 35654798 PMCID: PMC9163114 DOI: 10.1038/s41467-022-30769-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Accepted: 05/14/2022] [Indexed: 11/12/2022] Open
Abstract
Quantum phase transitions in quantum matter occur at zero temperature between distinct ground states by tuning a nonthermal control parameter. Often, they can be accurately described within the Landau theory of phase transitions, similarly to conventional thermal phase transitions. However, this picture can break down under certain circumstances. Here, we present a comprehensive study of the effect of hydrostatic pressure on the magnetic structure and spin dynamics of the spin-1/2 ladder compound C9H18N2CuBr4. Single-crystal heat capacity and neutron diffraction measurements reveal that the Néel-ordered phase breaks down beyond a critical pressure of Pc ∼ 1.0 GPa through a continuous quantum phase transition. Estimates of the critical exponents suggest that this transition may fall outside the traditional Landau paradigm. The inelastic neutron scattering spectra at 1.3 GPa are characterized by two well-separated gapped modes, including one continuum-like and another resolution-limited excitation in distinct scattering channels, which further indicates an exotic quantum-disordered phase above Pc. There is a class of quantum phase transitions that do not fit into the traditional Landau paradigm, but are described in terms of fractionalized degrees of freedom and emergent gauge fields. Hong et al. find evidence of such a transition in a molecular spin-1/2 antiferromagnetic ladder compound under hydrostatic pressure.
Collapse
Affiliation(s)
- Tao Hong
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
| | - Tao Ying
- School of Physics, Harbin Institute of Technology, 150001, Harbin, China
| | - Qing Huang
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, 37996, USA
| | - Sachith E Dissanayake
- Department of Mechanical Engineering, University of Rochester, Rochester, NY, 14617, USA
| | - Yiming Qiu
- National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA
| | - Mark M Turnbull
- Carlson School of Chemistry and Biochemistry, Clark University, Worcester, MA, 01610, USA
| | - Andrey A Podlesnyak
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Yan Wu
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Huibo Cao
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Yaohua Liu
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.,Second Target Station, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Izuru Umehara
- Department of Physics, Yokohama National University, Yokohama, 240-8501, Japan
| | - Jun Gouchi
- Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
| | - Yoshiya Uwatoko
- Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
| | - Masaaki Matsuda
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - David A Tennant
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, 37996, USA.,Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA
| | - Gia-Wei Chern
- Department of Physics, University of Virginia, Charlottesville, VA, 22904, USA
| | - Kai P Schmidt
- Lehrstuhl für Theoretische Physik I, Friedrich-Alexander-Universität (FAU) Erlangen-Nürnberg, Staudtstrasse 7, Erlangen, D-91058, Germany
| | - Stefan Wessel
- Theoretische Festkörperphysik, JARA-FIT and JARA-HPC, RWTH Aachen University, 52056, Aachen, Germany
| |
Collapse
|
2
|
Zhang Q, Li T. Why the Schwinger boson mean field theory fails to describe the spin dynamics of the triangular lattice antiferromagnetic Heisenberg model? JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:375601. [PMID: 34181593 DOI: 10.1088/1361-648x/ac0f2d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 06/28/2021] [Indexed: 06/13/2023]
Abstract
We find that the Schwinger boson mean field theory (SBMFT) supplemented with Gutzwiller projection provides an exceedingly accurate description for the ground state of the spin-12triangular lattice antiferromagnetic Heisenberg model (spin-12TLHAF). However, we find the SBMFT fails even qualitatively in the description of the dynamical behavior of the system. In particular, the SBMFT fails to predict the Goldstone mode in the magnetic ordered phase. We show that the coherent peak in the two-spinon continuum in the presence of spinon condensate should not be interpreted as a magnon mode. The SBMFT also predicts incorrectly a gapless longitudinal spin fluctuation mode in the magnetic ordered phase. We show that these failures are related to the following facts: (1) spinon condensation fails to provide a consistent description of the order parameter manifold of the 120 degree ordered phase. (2) There lacks in the SBMFT the coupling between the uncondensed spinon and the spinon condensate, which breaks both the spin rotational and the translational symmetry. (3) There lacks in the SBMFT the rigidity that is related to the no double occupancy constraint on the spinon system. We show that such failures of the SBMFT is neither restricted to the spin-12TLHAF nor to the magnetic ordered phase. We proposed a generalized SBMFT to resolve the first two issues and a new formalism to address the third issue.
Collapse
Affiliation(s)
- Qiu Zhang
- Department of Physics, Renmin University of China, Beijing 100872, People's Republic of China
| | - Tao Li
- Department of Physics, Renmin University of China, Beijing 100872, People's Republic of China
| |
Collapse
|