# Topological Insulators and Nematic Phases from Spontaneous Symmetry Breaking in

## Abstract

We investigate the stability of a quadratic band-crossing point (QBCP) in 2D fermionic systems. At the non-interacting level, we show that a QBCP exists and is topologically stable for a Berry flux {-+}2{pi}, if the point symmetry group has either fourfold or sixfold rotational symmetries. This putative topologically stable free-fermion QBCP is marginally unstable to arbitrarily weak shortrange repulsive interactions. We consider both spinless and spin-1/2 fermions. Four possible ordered states result: a quantum anomalous Hall phase, a quantum spin Hall phase, a nematic phase, and a nematic-spin-nematic phase.

- Authors:

- Publication Date:

- Research Org.:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)

- Sponsoring Org.:
- USDOE

- OSTI Identifier:
- 981390

- Report Number(s):
- SLAC-PUB-14078

TRN: US1003922

- DOE Contract Number:
- AC02-76SF00515

- Resource Type:
- Journal Article

- Journal Name:
- Submitted to Physical Review Letters

- Additional Journal Information:
- Journal Name: Submitted to Physical Review Letters

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; FERMIONS; INTERACTIONS; SPIN; STABILITY; SYMMETRY BREAKING; SYMMETRY GROUPS; MATSCI

### Citation Formats

```
Sun, K.
```*Topological Insulators and Nematic Phases from Spontaneous Symmetry Breaking in*. United States: N. p., 2010.
Web.

```
Sun, K.
```*Topological Insulators and Nematic Phases from Spontaneous Symmetry Breaking in*. United States.

```
Sun, K. Wed .
"Topological Insulators and Nematic Phases from Spontaneous Symmetry Breaking in". United States. https://www.osti.gov/servlets/purl/981390.
```

```
@article{osti_981390,
```

title = {Topological Insulators and Nematic Phases from Spontaneous Symmetry Breaking in},

author = {Sun, K},

abstractNote = {We investigate the stability of a quadratic band-crossing point (QBCP) in 2D fermionic systems. At the non-interacting level, we show that a QBCP exists and is topologically stable for a Berry flux {-+}2{pi}, if the point symmetry group has either fourfold or sixfold rotational symmetries. This putative topologically stable free-fermion QBCP is marginally unstable to arbitrarily weak shortrange repulsive interactions. We consider both spinless and spin-1/2 fermions. Four possible ordered states result: a quantum anomalous Hall phase, a quantum spin Hall phase, a nematic phase, and a nematic-spin-nematic phase.},

doi = {},

journal = {Submitted to Physical Review Letters},

number = ,

volume = ,

place = {United States},

year = {2010},

month = {5}

}

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