0:00:06three dimensional topological insulator is a fundamentally new phase electronic matter that is captured a
0:00:12lot of interest and the condensed matter physics community over the past two or three
0:00:15years
0:00:16fundamental interest and three topological slayers
0:00:19lies in the fact that exhibit a rare type behaviour called topological order
0:00:24which describes organized movement of electrons the crystal
0:00:27a consequence of this is that their surface electronics spectrums qualitatively distinct from any ordinary
0:00:33material
0:00:34in such a way is to allow us to select constant flow would not be
0:00:37tracked by impurities
0:00:40first experimental discovery but really talk much translator was making apply this that in and
0:00:45money i think he has sounds group of princeton university falling really prediction by charles
0:00:51cans collaborators at the university of pennsylvania
0:00:54the prediction was based on the idea that pure and the money which is a
0:00:57metal would become a topological insulator taken this newly formed into an insulator
0:01:03outgoing edge when you would there's no
0:01:05was predicted to perform this the defamation
0:01:08to test for the topological slater phase the has a group search for the distinguishing
0:01:13features of the serb select runs is a window into the box topological properties
0:01:18in a general insulated with been or be coupling there can be seen or insert
0:01:22states that standard log energy get is shown in this diagram
0:01:26for an ordinary insulator these of the state always discourse such that they form even
0:01:31number for me services
0:01:34topological insulator however the number of surface form is services are
0:01:38if even right count
0:01:40is a topological distinction and it is clear that this method can only relies on
0:01:44the material in a console
0:01:48in this paper we address the question of whether they're experimental signatures the topological order
0:01:53even in pure and to money
0:01:55because it's money metallic surface take only relies on being able to separate surface reebok
0:02:00states that the from the energy
0:02:02the technique we need to do this is an angle result photo emission spectroscopy
0:02:07the basic principles that photons intentional crystal bands money and excite electrons into the backing
0:02:13by measuring the energy momentum these further we electrons the energy momentum dispersion inside the
0:02:19crystal can be deduced
0:02:21two measures then these energy and momentum analyzed electrons an accelerated towards the heavy scattering
0:02:27target
0:02:28where they will be preferential e scattered left to right based on there's interaction going
0:02:33to standard scattering
0:02:35the distinguishing properties of statistics are that there's and colourised and have no dispersion one
0:02:41a direction normal to the surface
0:02:43a typical for emission spectrum of an someone you shown here along momentum cut denoted
0:02:47by the red line
0:02:49if we look at how the state that for me energy change against bearing on
0:02:53another one surface normal direction we find it only for right branches around zero momentum
0:02:57show no dispersion
0:03:00also find that these four ranges are still polarised proving that there indeed surfaced
0:03:05there are two possible ways these service states comes first which reflect whether enter non-use
0:03:10topological or not
0:03:11if the word topological and the surface states as first in the sense shown in
0:03:15the upper panel informant had a like for me services it on the right
0:03:20if you were not topological the surface data disposition below and instead form a concentric
0:03:25circular from is this
0:03:27the dispersion certain states overall momentum space
0:03:31we experimentally find that the from step is exhibited had a light all g which
0:03:35confirms that and twenty the d topological
0:03:38our here shows that even in metal there can be signatures a topological order
0:03:43it also confirmed that topological properties of is intentionally three topological and sliders the right
0:03:49from the electronic structure event
0:03:52in future this procedure can be generally applied to search for her materials a topological
0:03:56insulator