Spin Peierls transition of J1 - J2 and extended models with ferromagnetic J1

Datum

20.06.2023

Zeit

11:00 - 12:00

Sprecher

Manodip Routh

Zugehörigkeit

Bose National Centre for Basic Science / Guest in ITF

Sprache

en

Hauptthema

Materialien

Host

Grit Rötzer

Beschreibung

The spin-1/2 chain with ferromagnetic exchange J1 < 0 between first neighbors and antiferromagnetic J2 > 0 between second neighbors supports two spin-Peierls (SP) instabilities depending on the frustration alpha = J2/| J1|. Instead of chain dimerization with two spins per unit cell, J1-J2 models with alpha > 0.65 and linear spin-phonon coupling are unconditionally unstable to sublattice dimerization with four spins per unit cell. Unequal J1 to neighbors to the right and left extends the model to gapped (gamma > 0) chains with conditional SP transitions at TSP to dimerized sublattices and a weaker specific heat C(T) anomaly. The spin susceptibility chi(T) and C(T) are obtained in the thermodynamic limit by a combination of exact diagonalization of small systems with alpha > 0.65 and density matrix renormalization (DMRG) calculations of systems up to N ~ 100 spins. Both J1-J2 and gamma > 0 models account quantitatively for chi(T) and C(T) in the paramagnetic phase of beta-TeVO4 for T > 8 K, but lower T indicates a gapped chain instead of a J1-J2 model as previously thought. The same parameters and TSP = 4.6 K generate a C(T)/T anomaly that reproduces the anomaly at the 4.6 K transition of beta-TeVO4, but not the weak chi(T) signature. In this talk, I will give brief introduction on the Hybrid ED/DMRG technique which can be deployed to analyze the thermodynamics of low dimensional spin systems. I will talk about how sublattice dimerization leads to the spin Peierls transition of J1 - J2 and extended models with ferromagnetic J1 . Reference: [1] M. Routh, S. K. Saha, M. Kumar, and Z. G. Soos, Phys. Rev. B 105, 235109 (2022). .

Links

• Seminars at the IFW

Letztmalig verändert: 13.06.2023, 07:39:30