# Guo Chuan Thiang

## Contact Details

NameGuo Chuan Thiang |
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## Pubs By Year |
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## Pub CategoriesMathematics - Mathematical Physics (11) Mathematical Physics (11) High Energy Physics - Theory (10) Physics - Mesoscopic Systems and Quantum Hall Effect (7) Quantum Physics (3) Mathematics - Differential Geometry (3) Physics - Other (2) Mathematics - Operator Algebras (2) Mathematics - K-Theory and Homology (1) Mathematics - Quantum Algebra (1) Physics - Strongly Correlated Electrons (1) |

## Publications Authored By Guo Chuan Thiang

In semimetals with time-reversal symmetry, the interplay between Weyl points and Fu-Kane-Mele indices results in coexisting surface Dirac cones and Fermi arcs that are transmutable without a topological phase transition. The Weyl points' connectivity is essential for capturing the full topology of semimetals and their role as intermediaries of topological insulator transitions. We also predict the possibility of a topological Dirac cone on the interface between two Weyl semimetals. Read More

The subtle interplay between local and global charges for topological semimetals exactly parallels that for singular vector fields. Part of this story is the relationship between cohomological semimetal invariants, Euler structures, and ambiguities in the torsion of manifolds. Dually, a topological semimetal can be represented by Euler chains from which its surface Fermi arc connectivity can be deduced. Read More

We provide a manifestly topological classification scheme for generalised Weyl semimetals, in any spatial dimension and with arbitrary Weyl surfaces which may be non-trivially linked. The classification naturally incorporates that of Chern insulators. Our analysis refines, in a mathematically precise sense, some well-known 3D constructions to account for subtle but important global aspects of the topology of semimetals. Read More

**Affiliations:**

^{1}Oxford,

^{2}Adelaide,

^{3}Adelaide

We state and prove a general result establishing that T-duality simplifies the bulk-boundary correspondence, in the sense of converting it to a simple geometric restriction map. This settles in the affirmative several earlier conjectures of the authors, and provides a clear geometric picture of the correspondence. In particular, our result holds in arbitrary spatial dimension, in both the real and complex cases, and also in the presence of disorder, magnetic fields, and H-flux. Read More

We state a general conjecture that T-duality trivialises a model for the bulk-boundary correspondence in the parametrised context. We give evidence that it is valid by proving it in a special interesting case, which is relevant both to String Theory and to the study of topological insulators with defects in Condensed Matter Physics. Read More

**Affiliations:**

^{1}Adelaide,

^{2}Adelaide

Recently we introduced T-duality in the study of topological insulators, and used it to show that T-duality trivialises the bulk-boundary correspondence in 2 dimensions. In this paper, we partially generalise these results to higher dimensions and briefly discuss the 4D quantum Hall effect. Read More

**Affiliations:**

^{1}U. Adelaide,

^{2}U. Adelaide

Recently we introduced T-duality in the study of topological insulators. In this paper, we study the bulk-boundary correspondence for three phenomena in condensed matter physics, namely, the quantum Hall effect, the Chern insulator, and time reversal invariant topological insulators. In all of these cases, we show that T-duality trivializes the bulk-boundary correspondence. Read More

Topological insulators and D-brane charges in string theory can both be classified by the same family of groups. In this paper, we extend this connection via a geometric transform, giving a novel duality of topological insulators which can be viewed as a condensed matter analog of T-duality in string theory. For 2D Chern insulators, this duality exchanges the rank and Chern number of the valence bands. Read More

Equivalence classes of gapped Hamiltonians compatible with given symmetry constraints, such as those underlying topological insulators, can be defined in many ways. For the non-chiral classes modelled by vector bundles over Brillouin tori, physically relevant equivalences include isomorphism, homotopy, and $K$-theory, which are inequivalent but closely related. We discuss an important subtlety which arises in the chiral Class AIII systems, where the winding number invariant is shown to be relative rather than absolute as is usually assumed. Read More

**Authors:**Guo Chuan Thiang

We present a rigorous and fully consistent $K$-theoretic framework for studying gapped topological phases of free fermions such as topological insulators. It utilises and profits from powerful techniques in operator $K$-theory. From the point of view of symmetries, especially those of time reversal, charge conjugation, and magnetic translations, operator $K$-theory is more general and natural than the commutative topological theory. Read More

Complete sets of mutually unbiased bases are only known to exist in prime-power dimensions. We will describe a few approaches to the problem proving the (non)-existence of four mutually unbiased bases in dimension 6. These will include the notions of Grassmannian distance, quadratic matrix programming, semidefinite relaxations to polynomial programming, as well as various tools from algebraic geometry. Read More

We investigate the problem of finding the optimal convex decomposition of a bipartite quantum state into a separable part and a positive remainder, in which the weight of the separable part is maximal. This weight is naturally identified with the degree of separability of the state. In a recent work, the problem was solved for two-qubit states using semidefinite programming. Read More

We use the language of semidefinite programming and duality to derive necessary and sufficient conditions for the optimal Lewenstein-Sanpera Decomposition (LSD) of 2-qubit states. We first provide a simple and natural derivation of the Wellens-Kus equations for full-rank states. Then, we obtain a set of necessary and sufficient conditions for the optimal decomposition of rank-3 states. Read More