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**Dr. Ivan Naumov**

Geophysical Laboratory, Carnegie Institution of Sciences, 5251 Broad Branch Road, Washington DC 20015

March 19, 3:30 PM

Thirkield Hall (Physics), room 103

Topological phases: from topological insulators to compressed hydrogen and alkali metals

The recently established concept of
“topological phases” refers to the materials with a nontrivial
bulk-edge/surface correspondence of topological nature. In the context
of solid state physics, such phases include quantum Hall insulators,
topological insulators, topological semimetals, etc. In my talk, I will
first review the theoretical foundation for different topological
phases. I will discuss my recent results proving

that compressed
hydrogen and alkali metals can also be viewed as topological phases
under some conditions. I will show that both

dense hydrogen and
insulating forms of alkali metal (or high-pressure “electrides”) have
metallic surfaces that are controlled by the topology of the bulk band
structure; i.e., they are topological phases. Such surface-states
appear inside the bulk “direct” gap in the two-dimensional surface
Brillouin zone.

**Refreshments will be served ****at 3:15pm**