TUNNELING OF A HEAVY-PARTICLE WITH SPIN IN A METAL

The low-temperature behavior of a two-level system (TLS) with spin is investigated, where the atom tunneling between two positions possesses a spin and interacts with the conduction electrons by an exchange int eraction. To describe the physical properties of this TLS a generalize d model is developed, where in addition to the usual screening and ele ctron assisted tunneling processes exchange interaction and exchange a ssisted interactions with the conduction electrons are introduced. The se exchange interaction terms break the SU(2) symmetry of the original TLS model corresponding to the conduction-electron spin. Summing up t he leading logarithmic vertex corrections we show that if the Kondo te mperature associated with the orbital degrees of freedom, T-K(orb), is smaller than that associated with the exchange interaction, T-K(magn) , then the orbital degrees of freedom of the TLS are frozen out when t he magnetic Kondo effect takes place and only a magnetic Kondo effect occurs. In this case the ground state of the system seems to be a Ferm i-liquid state. In the opposite case, T-K(orb) > T-K(magn) two orbital electron channels become dominant below T-K(orb) and a new fixed poin t appears. The possibility of experimental realizations is also shortl y discussed.