scholarly journals Pressure-induced normal-incommensurate-commensurate phase transitions in TiPO4

2014 ◽  
Vol 70 (a1) ◽  
pp. C263-C263 ◽  
Author(s):  
Maxim Bykov ◽  
Elena Bykova ◽  
Leonid Dubrovinsky ◽  
Michael Hanfland ◽  
Hanns-Peter Liermann ◽  
...  
Keyword(s):  
High Pressure ◽  
Phase Transitions ◽  
Degrees Of Freedom ◽  
Spin Exchange ◽  
Exchange Interactions ◽  
Quantum Spin ◽  
Singlet Ground State ◽  
Transition Temperatures ◽  
Spin Lattice ◽  
Commensurate Phase

The complex interplay between spin, charge, orbital, and lattice degrees of freedom has made low-dimensional quantum spin magnets with strong antiferromagnetic (AF) spin-exchange coupling prime candidates for studying unusual magnetic phenomena. A progressive spin-lattice dimerization in one-dimensional AF Heisenberg chains, which occurs below a critical temperature and induces a singlet ground state with a magnetic gap, is commonly referred to as spin-Peierls (SP) transition. Recently, the compounds TiOX (X = Cl, Br) and TiPO4have been intensively investigated due to their unconventional behavior [1,2]. Unlike standard SP systems, TiOX and TiPO4undergo a sequence of normal-incommensurate-commensurate phase transitions on cooling at remarkably high transition temperatures. The transition temperatures are related to the direct exchange interactions between Ti ions, which increases strongly with decreasing the distance between the Ti ions, and therefore is very sensitive to the applied hydrostatic pressure. We have performed pressure-dependent single-crystal X-ray diffraction of TiPO4using synchrotron radiation. TiPO4undergoes a pressure-induced pahse transiton towards an incommensurate phase already below 10 GPa. This transformation is followed by the lock-in phase transition to the dimerized SP phase. Both structures are analogous to those at low temperatures, but reveal significantly larger modulation amplitudes. In this contribution we will present the detailed discussion of the high-pressure structures of TiPO4and their behavior on compression. Furthermore, similarities and differences of high-pressure phase diagrams of TiOCl and TiPO4and discrepancies between predicted and observed structures will be considered.

EXACT SOLUTIONS IN A SPATIALLY ANISOTROPIC QUANTUM SPIN LADDER MODEL HAVING TWO- AND FOUR-SPIN EXCHANGE INTERACTIONS

2009 ◽  
Vol 23 (08) ◽  
pp. 1981-2019 ◽  
Author(s):  
J. H. BARRY ◽  
J. D. COHEN ◽  
M. W. MEISEL
Keyword(s):  
Spin Exchange ◽  
Inelastic Neutron Scattering ◽  
Exchange Interactions ◽  
Inelastic Neutron ◽  
Elementary Excitation ◽  
Quantum Spin ◽  
Quantum Model ◽  
Spin Ladder ◽  
Zero Field ◽  
Ladder Model

We consider a two-leg S=1/2 quantum spin ladder model with two-spin (intra-rung) and four-spin (inter-rung) Heisenberg exchange interactions and a uniform magnetic field. Exact mappings are derived connecting the partition function and correlations in the three-parameter quantum model to those known in a two-parameter Ising chain. The quantum phase diagram of the ladder magnet is determined. Static correlations provide pertinent correlation lengths and underlie spatial fluctuation behaviors at arbitrary temperatures, including quantum fluctuations at absolute zero. Dynamic correlations in zero field are used to obtain an exact solution for the inelastic neutron scattering function Sxx(q, ω) at all temperatures, explicitly yielding the elementary excitation spectrum.

scholarly journals Quantum spin dynamics with pairwise-tunable, long-range interactions

2016 ◽  
Vol 113 (34) ◽  
pp. E4946-E4955 ◽  
Author(s):  
C.-L. Hung ◽  
Alejandro González-Tudela ◽  
J. Ignacio Cirac ◽  
H. J. Kimble
Keyword(s):  
Spin Exchange ◽  
Spin Dynamics ◽  
Explicit Construction ◽  
Quantum Spin ◽  
Interaction Coefficients ◽  
Spin Models ◽  
Spin Lattice ◽  
Full Control ◽  
Spin Interactions ◽  
Atomic States

We present a platform for the simulation of quantum magnetism with full control of interactions between pairs of spins at arbitrary distances in 1D and 2D lattices. In our scheme, two internal atomic states represent a pseudospin for atoms trapped within a photonic crystal waveguide (PCW). With the atomic transition frequency aligned inside a band gap of the PCW, virtual photons mediate coherent spin–spin interactions between lattice sites. To obtain full control of interaction coefficients at arbitrary atom–atom separations, ground-state energy shifts are introduced as a function of distance across the PCW. In conjunction with auxiliary pump fields, spin-exchange versus atom–atom separation can be engineered with arbitrary magnitude and phase, and arranged to introduce nontrivial Berry phases in the spin lattice, thus opening new avenues for realizing topological spin models. We illustrate the broad applicability of our scheme by explicit construction for several well-known spin models.

scholarly journals Thermodynamics of General Heisenberg Spin Tetramers Composed of Coupled Quantum Dimers

2021 ◽  
Vol 7 (2) ◽  
pp. 29
Author(s):  
Peter Dyszel ◽  
Jason T. Haraldsen
Keyword(s):  
Quantum Computing ◽  
Data Storage ◽  
Spin Exchange ◽  
Energy Levels ◽  
Exchange Interactions ◽  
Analytic Solutions ◽  
Quantum Spin ◽  
Molecular Magnets ◽  
Heisenberg Spin ◽  
Schottky Anomaly

Advances in quantum computing technology have been made in recent years due to the evolution of spin clusters. Recent studies have tended towards spin cluster subgeometries to understand more complex structures better. These molecular magnets provide a multitude of phenomena via exchange interactions that allow for advancements in spintronics and other magnetic system applications due to the possibility of increasing speed, data storage, memory, and stability of quantum computing systems. Using the Heisenberg spin–spin exchange Hamiltonian and exact diagonalization, we examine the evolution of quantum energy levels and thermodynamic properties for various spin configurations and exchange interactions. The XXYY quantum spin tetramer considered in this study consists of two coupled dimers with exchange interactions α1J and α1′J and a dimer–dimer exchange interaction α2J. By varying spin values and interaction strengths, we determine the exact energy eigenstates that are used to determine closed-form analytic solutions for the heat capacity and magnetic susceptibility of the system and further analyze the evolution of the properties of the system based on the parameter values chosen. Furthermore, this study shows that the Schottky anomaly shifts towards zero as the ground-state of the system approaches a quantum phase transition between spin states. Additionally, we investigate the development of phase transitions produced by the convergence of the Schottky anomaly with both variable exchange interactions and external magnetic field.

scholarly journals Meson formation in mixed-dimensional t-J models

2018 ◽  
Vol 5 (6) ◽  
Author(s):  
Fabian Grusdt ◽  
Zheng Zhu ◽  
Tao Shi ◽  
Eugene Demler
Keyword(s):  
Transition Metal Oxides ◽  
Ultracold Atoms ◽  
Bound States ◽  
Degrees Of Freedom ◽  
Direct Evidence ◽  
Spin Exchange ◽  
Exchange Interactions ◽  
Charge Carriers ◽  
Quantum Gas ◽  
Complex Phenomena

Surprising properties of doped Mott insulators are at the heart of many quantum materials, including transition metal oxides and organic materials. The key to unraveling complex phenomena observed in these systems lies in understanding the interplay of spin and charge degrees of freedom. One of the most debated questions concerns the nature of charge carriers in a background of fluctuating spins. To shed new light on this problem, we suggest a simplified model with mixed dimensionality, where holes move through a Mott insulator unidirectionally while spin exchange interactions are two dimensional. By studying individual holes in this system, we find direct evidence for the formation of mesonic bound states of holons and spinons, connected by a string of displaced spins – a precursor of the spin-charge separation obtained in the 1D limit of the model. Our predictions can be tested using ultracold atoms in a quantum gas microscope, allowing to directly image spinons and holons, and reveal the short-range hidden string order which we predict in this model.

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