Effects of Two Energy Scales in Weakly Dimerized Antiferromagnetic Quantum Spin Chains

Abstract

By means of thermal expansion and specific heat measurements on the high-pressure phase of (VO)${}_2$P${}_2$O${}_7$, the effects of two energy scales of the weakly dimerized antiferromagnetic $S$ = 1/2 Heisenberg chain are explored. The low energy scale, given by the spin gap $\Delta$, is found to manifest itself in a pronounced thermal expansion anomaly. A quantitative analysis, employing T-DMRG calculations, shows that this feature originates from changes in the magnetic entropy with respect to $\Delta$, $\partial S^m/\partial \Delta$. This term, inaccessible by specific heat, is visible only in the weak-dimerization limit where it reflects peculiarities of the excitation spectrum and its sensitivity to variations in $\Delta$.

arXiv comment4 pages, 4 figures now identical with finally published version

References in corpus (10)

• Surprises on the Way from 1D to 2D Quantum Magnets: the Novel Ladder Materials
• Magnetization plateaus in spin chains: ``Haldane gap'' for half-integer spins
• Thermodynamics of Spin S = 1/2 Antiferromagnetic Uniform and Alternating-Exchange Heisenberg Chains
• Muffin Tin Orbitals of Arbitrary Order
• Universally diverging Grueneisen parameter and the magnetocaloric effect close to quantum critical points
• Magnetic Excitations in the S=1/2 Alternating Chain Compound (VO)_2P_2O_7
• A Study of the S=1/2 Alternating Chain using Multiprecision Methods
• High-resolution ac-calorimetry studies of the quasi-2D organic superconductor $\kappa$-(BEDT-TTF)${}_2$Cu(NCS)${}_2$
• Temperature driven crossover phenomena in the correlation lengths of the one-dimensional t-J model
• Modeling of the Magnetic Susceptibilities of the Ambient- and High-Pressure Phases of (VO)_{2}P_{2}O_{7}

Cited by in corpus (4)

• Lattice effects and entropy release at the low-temperature phase transition in the spin-liquid candidate $\kappa$-(BEDT-TTF)${}_2$Cu${}_2$(CN)${}_3$
• Evidence for Lattice Effects at the Charge-Ordering Transition in (TMTTF)${}_2$X
• Magnetic phase diagram of the multiferroic FeTe${}_2$O${}_5$Br
• Lattice effects in the quasi-two-dimensional valence-bond-solid Mott insulator EtMe${}_3$P[Pd(dmit)${}_2$]${}_2$