Alaric Sanders
About Me

I’m a third year physics PhD student at the University of Cambridge. I study strongly-correlated electrons and frustrated magnetism; materials in which conventional approximations about independent electrons break down and more interesting quantum behaviour can manifest.

My current research interest is in Quantum Spin Ice.

I am the current manager of Maggie’s Bar, the famed graduate bar of Christ’s College.

My Publications

In Plain English: There is a widely known theoretical model of pyrochlore compounds known as Quantum Spin Ice, in which it is expected that some materials (read: rocks) behave a lot like quantum electricity and magnetism at low temperatures. There is a growing body of evidence that some Cerium oxides, e.g. Ce$_2$Hf$_2$O$_7$, may be a real-life implementation of this model. In this work, we predicted that applying a weak magnetic field to some Cerium compounds should substantially tune the laws of physics in the material, and gave clear experimental signatures of the tuning to look for. Experimental observation of the signatures we predicted would substantially strengthen the current body of evidence for the real-life existence of quantum spin ice.

In Plain(ish) English: We dive deep into the idea of a quantum spin ice that is not symmetric under mirroring (where inversion symmetry is broken). Some preliminaries on quantum spin ice (QSI)

  1. QSI is a scale model of the theory of electricity and magnetism.
  2. QSI is host to three kinds of quasiparticle excitations: magnetic monopoles (spinons), spin waves (photons) and electrically charged Dirac monopoles (visons)

We find that, in the absence of inversion symmetry, it is possible to construct a spin ice phase that resembles a gas of free electrons moving in a crystal of magnetic monopoles. The model is unique in the literature, and has a first order phase transition with an unusual critical point.

In Plain(ish) English: There is a very interesting model of quantum magnetism in 2D materials: the “Kitaev Honeycomb”, after Alexei Kitaev. This model took the (physics) world by storm when it appeared in a legendary 2006 paper - it is a) exactly solvable, b) relatively simple to write down, and c) has excitations that are unlike any particle seen in nature – anyons. There are theoretical arguments to suggest that the compounds listed in the title of our work have exchange constants similar to the Kitaev model, however real materials always pollute this with non-ideal additional terms in the Hamiltonian that ruin the Kitaev physics.

Our work determines a range of acceptable coupling constants for these materials based on the results of a neutron scattering experiment. We point out that, due to an exact symmetry in the model we use, no neutron scattering experiment can uniquely determine the sign of the all-important Kitaev coupling constant. Instead, we present two equally-good models dual to one another by exact symmetry, and propose the use of a complementary technique (e.g. RIXS) to determine the sign of the Kitaev term uniquely.

Contact Me