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Samarium hexaboride (SmB 6 ) has recently been considered to be a topological Kondo insulator (TKI), the first strongly correlated electron system to exhibit topological surface conduction states. In this contribution, results of electrical resistivity measurements (T) between 80 K and 0.08 K of various SmB 6 single crystalline samples are presented, analyzed and discussed. The received results imply that the residual conductivity of SmB 6 below about 4 K is of non-activated (metallic-like) nature. It is shown that this metallic-like behaviour can be attributed both to surface (2D) conduction states, as may be expected in case of a topological insulator, as well as to the highly correlated many-body (3D) bulk ground state which is formed within the gap of this compound. From this it follows that in SmB 6 , where surface conductivity states are clearly present, there is in parallel also a bulk contribution to residual electrical conductivity originating from the strongly correlated electron system with valence fluctuations. This raises the question whether SmB 6 does not form a new / special type of topological insulator in which in the energy gap besides the surface conduction states, there is also a conducting narrow in-gap band originating from the bulk strongly correlated electron system.

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TmB4 is a Shastry-Sutherland frustrated system which exhibits very complex magnetic properties. In this contribution the phase diagram of magnetic eld vs. temperature of TmB4 under hydrostatic pressure up to 26.5 kbar is investigated using sensitive ac-resistance measurements. Temperature and magnetic eld dependences of resistance at various pressures were carried out in a piston cylinder pressure cell between 1.7 and 14 K and in magnetic elds up to 6 T. The obtained results exhibit shifts of ordering temperatures TN as well as shifts of boundaries between dierent magnetic phases. The observed pressure dependences of TN can be described by the relation d ln TN / dp = +(0.16 ÷ 0.18) %/kbar. The eect of pressure on various interactions between magnetic ions in this compound is discussed.