Spin and charge currents through contacted quantum spin chains: A time-dependent density matrix renormalization group study

• Applicants: Dr. Satoshi Ejima; Professor Dr. Holger Fehske
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 344071920

Antiferromagnetic metals and insulators are promising candidates for encoding, transferring and processing information in novel spintronic devices, which combine excellent performance, high sensitivity, low energy consumption and easy handling. In such systems the transmission of signals is rather mediated by spin currents, representing a flow of spin angular momentum, than by charge currents. To get spin currents into and out of the active antiferromagnetic component, the (inverse) spin Hall effect can be exploited in the electrical writing, reading, and switching processes. Within the scope of the proposed research project, we model such a generic spintronic setup by an (anisotropic) quantum spin (1/2 or 1) chain in an external magnetic field, sandwiched between two two- or three-dimensional leads (reservoirs) with strong Rashba- or Dresselhaus-type spin-orbit coupling at play, and calculate, in particular, the spin and charge currents through the device. To this end, we combine basically unbiased numerical techniques, the time-dependent density-matrix renormalization group method (in a matrix-product-state based formulation) with the block Lanczos recursion or tree tensor network schemes. The algorithm will be parallelized and implemented on large-scale compute clusters. In our theoretical approach, the spin-chain term facilitates both (more standard) ferromagnetic and antiferromagnetic situations, expected to show diffusive and ballistic transport behavior, respectively. Furthermore, depending on the anisotropy of the spin-spin interaction, a gapless or gapful state is realized by the driven spin chain, with notably different transport properties. Increasing the magnetic field strength in the latter case, the spin excitation gap will be reduced and finally closed, which provides one mean for tuning/control the spin current. In going beyond the hitherto existing (rather phenomenological) descriptions of spin-wave currents we are in the position to analyze and quantify intrinsic quantum effects in the spintronics of antiferromagnetic systems. We also envisage the investigation of spin-dependent transport through quantum spin-chains coupled to topological insulators.

• DFG Programme: Research Grants