# Exceptional points in classical spin dynamics

## Abstract

Abstract Non-conservative physical systems admit a special kind of spectral degeneracy, known as exceptional point (EP), at which eigenvalues and eigenvectors of the corresponding non-Hermitian Hamiltonian coalesce. Dynamical parametric encircling of the EP can lead to non-adiabatic evolution associated with a state flip, a sharp transition between the resonant modes. Physical consequences of the dynamical encircling of EPs in open dissipative systems have been explored in optics and photonics. Building on the recent progress in understanding the parity-time ( $${\mathscr{P}}{\mathscr{T}}$$ $PT$ )-symmetric dynamics in spin systems, we use topological properties of EPs to implement chiral non-reciprocal transmission of a spin through the material with non-uniform magnetization, like helical magnet. We consider an exemplary system, spin-torque-driven single spin described by the time-dependent non-Hermitian Hamiltonian. We show that encircling individual EPs in a parameter space results in non-reciprocal spin dynamics and find the range of optimal protocol parameters for high-efficiency asymmetric spin filter based on this effect. Our findings offer a platform for non-reciprocal spin devices for spintronics and magnonics.

- Authors:

- Publication Date:

- Research Org.:
- Argonne National Lab. (ANL), Argonne, IL (United States)

- Sponsoring Org.:
- USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division

- OSTI Identifier:
- 1619592

- Alternate Identifier(s):
- OSTI ID: 1578048

- Grant/Contract Number:
- AC02-06CH11357

- Resource Type:
- Published Article

- Journal Name:
- Scientific Reports

- Additional Journal Information:
- Journal Name: Scientific Reports Journal Volume: 9 Journal Issue: 1; Journal ID: ISSN 2045-2322

- Publisher:
- Nature Publishing Group

- Country of Publication:
- United Kingdom

- Language:
- English

- Subject:
- 36 MATERIALS SCIENCE

### Citation Formats

```
Galda, Alexey, and Vinokur, Valerii M. Exceptional points in classical spin dynamics. United Kingdom: N. p., 2019.
Web. https://doi.org/10.1038/s41598-019-53455-0.
```

```
Galda, Alexey, & Vinokur, Valerii M. Exceptional points in classical spin dynamics. United Kingdom. https://doi.org/10.1038/s41598-019-53455-0
```

```
Galda, Alexey, and Vinokur, Valerii M. Mon .
"Exceptional points in classical spin dynamics". United Kingdom. https://doi.org/10.1038/s41598-019-53455-0.
```

```
@article{osti_1619592,
```

title = {Exceptional points in classical spin dynamics},

author = {Galda, Alexey and Vinokur, Valerii M.},

abstractNote = {Abstract Non-conservative physical systems admit a special kind of spectral degeneracy, known as exceptional point (EP), at which eigenvalues and eigenvectors of the corresponding non-Hermitian Hamiltonian coalesce. Dynamical parametric encircling of the EP can lead to non-adiabatic evolution associated with a state flip, a sharp transition between the resonant modes. Physical consequences of the dynamical encircling of EPs in open dissipative systems have been explored in optics and photonics. Building on the recent progress in understanding the parity-time ( $${\mathscr{P}}{\mathscr{T}}$$ P T )-symmetric dynamics in spin systems, we use topological properties of EPs to implement chiral non-reciprocal transmission of a spin through the material with non-uniform magnetization, like helical magnet. We consider an exemplary system, spin-torque-driven single spin described by the time-dependent non-Hermitian Hamiltonian. We show that encircling individual EPs in a parameter space results in non-reciprocal spin dynamics and find the range of optimal protocol parameters for high-efficiency asymmetric spin filter based on this effect. Our findings offer a platform for non-reciprocal spin devices for spintronics and magnonics.},

doi = {10.1038/s41598-019-53455-0},

journal = {Scientific Reports},

number = 1,

volume = 9,

place = {United Kingdom},

year = {2019},

month = {11}

}

https://doi.org/10.1038/s41598-019-53455-0

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