Production of single crystals

Both compounds – NbAs and NbP – are topological Weyl semimetals, one of the most intensively studied classes of materials in condensed matter physics.

Together with the Institute of Applied Physics

The Institute of Applied Physics of Moldova State University is our official partner. Its researchers co-authored an international study of Weyl fermions in NbAs with colleagues from the USA, Germany and Japan (Applied Physics Letters, 2018).

The study used well-faceted NbAs crystals a few millimetres in size. They were grown at 850 °C by chemical vapour transport with iodine, with synthesis and growth combined in a single sealed quartz ampoule. X-ray diffraction confirmed the NbAs phase.

Why physicists study NbAs and NbP

In 2015, calculations predicted that NbAs, NbP and the related TaAs and TaP are Weyl semimetals: their electrons behave like massless Weyl particles, which have never been observed in particle physics. The same year, experiments confirmed the prediction: photoemission spectroscopy of NbAs crystals revealed Weyl fermions and the surface states associated with them – “Fermi arcs”.

The unusual electronic structure also shows in the transport properties. NbP was found to have ultrahigh carrier mobility and an extremely large magnetoresistance: 850,000% at 1.85 K in a 9 T magnetic field, and about 250% at room temperature.

Crystal structure

NbAs and NbP crystallise in a tetragonal lattice without a centre of inversion (space group I4₁md). The lack of an inversion centre is a necessary condition for Weyl points to exist in non-magnetic crystals.

Research applications

• magnetotransport: extremely large magnetoresistance, quantum oscillations, negative longitudinal magnetoresistance linked to the chiral anomaly;
• angle-resolved photoemission spectroscopy (ARPES): bulk Weyl points and surface Fermi arcs;
• ultrafast and infrared optics: the dynamics of photoexcited Weyl fermions.

How to order

Tell us which compound and how many samples you need, for which experiment, and what size the crystals should be. We will advise on the parameters and let you know the terms and delivery time.

Sources:

• C. P. Weber and co-authors, “Directly photoexcited Dirac and Weyl fermions in ZrSiS and NbAs”, Applied Physics Letters 113, 221906 (2018)
• H. Weng and co-authors, “Weyl Semimetal Phase in Noncentrosymmetric Transition-Metal Monophosphides”, Physical Review X 5, 011029 (2015)
• S.-Y. Xu and co-authors, “Discovery of a Weyl fermion state with Fermi arcs in niobium arsenide”, Nature Physics 11, 748 (2015)
• C. Shekhar and co-authors, “Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal candidate NbP”, Nature Physics 11, 645 (2015)