FORUM DQMP

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Date(s) - 15/12/2015
13 h 00 min - 14 h 00 min

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FORUM DQMP

Tuesday, December 15, 2015 – 13h00

Auditoire Stückelberg – Ecole de physique

 

Coffee and tea will be available from

12h50 at the entrance of the Auditoire

 

Tuning magnetotransport in a compensated semimetal

at the atomic scale

Lin Wang (group of Prof. Morpurgo)

 

Either in bulk form, or when exfoliated into atomically thin crystals, layered transition metal

dichalcogenides are continuously leading to the discovery of new phenomena. The latest example is

provided by 1T’-WTe2, a semimetal found to exhibit the largest known magnetoresistance in bulk, and

predicted to become a topological insulator in strained monolayers. Here we show reducing the

thickness by exfoliation provides an effective experimental knob to tune the electronic properties of

WTe2, which allows us to identify the microscopic mechanisms responsible for the classical and

quantum magnetotransport down to the ultimate atomic scale. We find that the longitudinal and the Hall

resistance are reproduced quantitatively in terms of a classical two-band model for crystals as thin as

six layers, and that for thinner crystals a crossover to an insulating Anderson-localized state occurs.

Our results represent a complete validation of two-band theory, and indicate that atomically thin WTe2

remain gapless semimetals, from which we conclude that searching for a topological insulating state by

straining monolayers is a challenging, but feasible experiment.

 

Fast ion conduction and doping mechanism

in garnet-type metal borohydrides

Matteo Brighi (group of Prof. Cerny)

 

Complex hydrides are a family of compounds which have attracted a lot of attention in last decade for

various clean energy-related applications, from solid state hydrogen storage to materials suitable for Lior

Na-ion batteries. Concerning the latter, the replacement of liquid by solid state electrolytes is one of

the key issues in the development of the next generation of batteries.

We present two new garnet-type borohydrides suitable as solid state electrolytes:

Li3K3Ce2(BH4)12 and Li3K3La2(BH4)12 show unexpectedly high room temperature Li+ ionic conductivity

(when compared to reported isostructural garnet oxide Li+ conductors) of 3×10-7 and 6×10-7 S/cm.

The effect of heterovalent cation substitution is investigated as means of tailoring ionic conductivity.

Doping with divalent Sr2+ and Eu2+ shows increase of Li+ ionic conductivity by one order of magnitude

in the whole temperature range measured.

 

Forum Committee : L. Foini, C. Lichtensteiger, N. Ubrig (3.12.2015)

Réalisation : Sur Mesure concept